Podiatrist vs. pedometer vs. pedophile?

You can answer this question by looking at the various etymologies of the words. A useful resource for looking up etymologies is Etymonline.com, which gives the following:

pedometer (n.)

instrument for measuring distances covered by a walker, 1723, from French pédomètre (1712), a hybrid coined from Latin pedis (genitive of pes "foot;" see foot (n.)) + Greek metron "a measure" (see meter (n.2)). At first Englished as waywiser.

and

pedophile (n.)

1951, derived noun from pedophilia.

and

pedophilia (n.)

1900, from Greek pais (genitive paidos) "child" (see pedo-) + philos "loving" see -phile). First attested in an abstract of a report by Krafft-Ebing.

As you can see, pedometer comes from Latin via French. The Latin root is pedis (notice the 'd'), meaning "of feet".

Pedophile comes from Greek. The root is paidos (notice the 'd'), meaning "of children."

Don't make the mistake of thinking every time you see pedo- in a word, it means "of children". Sometimes it means "of children" (following the Greek etymology) and sometimes it means "of feet" (following the Latin etymology).

The same goes for pod-. You have to look at the specific etymologies to see where the prefix is coming from originally.

The etymology of the word "pedophile" as I know it is fraught with peril. As I recall it, the word should be spelled and pronounced as pædophile.

In print, you can see the word paedophile in the Collins English Dictionary – Complete and Unabridged, 12th Edition. The paedophile spelling goes back as far as 1908, whereas the pedophile spelling only started appearing in 1944 according to the Google Ngrams library. It looks like the word was just too difficult to properly enunciate for most people, so the spelling was changed to reflect the common pronunciation when it started becoming popularized amongst the general public.

However those ae/æ words have been seemingly evicted from the language. Yeah, the Encyclopædia Britanica still uses the Encyclopædia spelling and have been since at least the 9th edition which is significant but as far as I know everybody else, including the now much more known Wikipedia, the free Encyclopedia uses the alternate spelling. The Google nGrams are pretty condemning here too as the Encyclopædia spelling has been declining in isolation from the other variants and isn't even a blip on the radar by means of comparison if you discount what's arguably the most significant historical use of the word.

Do note that this makes so much more sense with The Online Etymology Dictionary etymology entry Silenus already mentioned:

1900, from Greek pais (genitive paidos) "child" (see pedo-) + philos "loving" see -phile). First attested in an abstract of a report by Krafft-Ebing.

The emphasis is my own, to emphasize the probable pronunciation of the word-forming element we probably should be using, if people weren't lazy and the cause wasn't hopeless. Oh well, at least it's not like pedophile ever meant anything else in English as far as I know, although it does seem to deny foot fetishists the unique single word they should rightfully own (which is not to say that anybody would want the name at this point anyway). Regardless, if not only in order to further emphasize this point, let's go look at the referenced entry at The Online Etymology Dictionary too:

Pedo before vowels ped-, word-forming element meaning "boy, child," from Greek pedo-, comb. form of pais "boy, child," especially a son, from PIE root *peu- "small, little, few, young" (see few (adj.)). The British form paed- is better because it avoids confusion with ped-.

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paedo- see pedo-.

A recent use of the word can be found in Stop Using the Word Paedophile, written by Julie Bindel for The Guardian.

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Citations and Alternate links:

Wiktionary entries for pædophile and encyclopædia, reproduced on Wordnik.

The Collins English Dictionary – Complete and Unabridged, 12th Edition's entry for paedophile.

As stated by Stop Using the Word Paedophile, written by Julie Bindel for The Guardian and published Tuesday 23 May 2006: Archived on The Internet Archive's Wayback Machine

This is the present Encyclopædia Britanica's homepage, archived on The Internet Archive's Wayback Machine

There is a photograph on The Dull but Dependable Encyclopaedia Britannica Bows to the Digital Facts of Life by Max Davidson for The Telegraph 14 Mar 2012, archived on The Internet Archive's Wayback Machine

This is Wikipedia Homepage, 31 Mar 01 snapshot, archived on The Internet Archive's Wayback Machine

This is a Screenshot of the Google Ngrams Usage Trends Comparison for, Encyclopaedia, Encyclopædia and encyclopedia.

This is Screenshot of the Google Ngrams Usage Trends Comparison for Paedophile, Pedophile

This is a Google nGrams Screenshot for the usage trend of Encyclopædia, which is isolated from other words

This is The Online Etymology Dictionary's Entry for pedophile: Archived on The Internet Archive's Wayback Machine

This is The Online Etymology Search Results Page for pedo-, with the paedo wordforming element

Here are scholarly citations for The Online Etymology Dictionary, and an archival link to them The Internet Archive's wayback machine.

You got two different Ablaut grades of the same root, plus a different root here.

One root is Proto-Indo-European *ped- 'foot', as noted. This comes in two varieties:

• the E-grade, represented in Latin pedis 'foot', with root ped-
• the O-grade, represented in Greek podos 'foot', with root pod-

English borrowed lots of words with both of these roots:
podiatrist (< Gk iatros, 'physician'), podium, pedal, pedometer (< Lat meter 'measure').

The other root is PIE *pau- 'small; child', the source of Latin parvus 'small',
and Greek paidos 'child'. Words from Greek and Latin with AI or AE in them
tended to be borrowed into English with an E, so we get words from paidos like

• pediatrician (< Gk iatros, 'physician')
  pedagogue (< Gk agogos, 'leader')
  pedophile (< Gk philos, 'love')

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Postnote: The Latin root pod is the same as the pre-Germanic root, but all the Germanic languages went through a series of regular sound changes called "Grimm's Law", in which
PIE *p changed to f, and PIE *d changed to t, leaving the Proto-Germanic root *fot-,
which is the source of English foot.

Same thing for pater and father, (*t changed to th) canis and hound (*k changed to h),
cardium and heart, etc. If you understand Grimm's Law, you double your English vocabulary.

Also I think you're confusing the way o Meter works as a suffix. Kind of like a speedometer or a tachometer, it is Ped-ometer. Not pedo-meter.

Overwhelmingly, it is considered that paedophilia (although I can't attest to the spelling 100% as I do not have an original copy of the work) was first used in print in Richard von Krafft-Ebing's 'Psychopathia Sexualis'. One assumes that as much of this tome was written in Latin and Greek he would be quite knowledgeable in these languages. So I imagine that the reason he did NOT use 'paedophilia' (or 'pedophilia') to describe a sexual attraction to prepubescent children is because he knew that that's not what it meant. What he did do was to use the word in conjunction with the qualifying term 'erotica' to describe this condition as he saw it.

In fact there are many Greek words for love, although it's usually the four main ones that are commonly cited; Storge – empathy bond. Philia – friend bond. Eros – romantic love. Agape – unconditional "God" love.

This is probably largely as a result of C. S. Lewis's fascination in his 'The Four Loves'.

It's interesting to note that the -phile suffix is commonly used in a more objectively understood way than "friend bond". Such as in 'Francophile', 'Bibliophile', 'Oenophile' etc. So as that I would expect 'Paedophile' to mean an objective but respectful interest in the subject of children. The same could be said for other words that have evolved a sexual connotation such as 'Necrophile' (eg: a Taxidermist) and 'Zoophile' (eg: David Attenborough).

One last point; many of these sexualised terms are grouped together under the heading 'Paraphilias'. Far from contradicting the above argument; para-, used here, infers "abnormal". Therefore, it is describing something that is not a true, normal, -philia, so thus it is effectively not a -philia.