Does "eff" mean to describe in words?

If one dissects the word “ineffable”, there are three main roots

• in – not
• able – able to be done
• eff

The meaning of the root able implies that some part of the word before it must refer to an action. Given that in is solely and adverb in this case, that would, by default, make eff a verb. Knowing that eff is a verb with a meaning antonymic to the word as a whole, I assume that it means something to the effect of “to describe in words”

However, I have not yet found a dictionary that acknowledges this. They have acknowledged “effable”,but not “eff”. Is it simply a quirk of our language that the word is never used, or has my logic failed me somewhere?