What is the meaning of "I am so fly"?

In the 1939 novel, The Grapes Of Wrath, ‘feeling fly’ is used to mean being sexually excited.

All it means when we say it is that something is cool or that it looks good. In example I have a shirt that says stay fly. It is simply stating that you should stay in style.

In US hip hop slang, both "competent / skilled" and "sexy".

The "Fly Girls" were the dancers on "In Living Color" in the early 90's, but the term is much older.

Since the word is used with this meaning as part of the title of the 1971 film "Super Fly", it must come from the late 1960's at the latest, and could easily predate that.

(3) fly
adjective

(slang)
(mainly British) knowing and sharp; smart
(mainly Scottish) furtive or sneaky

C19: of uncertain origin

[ Collins English Dictionary Online - "fly" ]

---

(3) fly

adj.
1. Chiefly British Mentally alert; sharp.
2. Slang Fashionable; stylish.

[ AmHDotEL - "fly" ]

---

fly (adj.) slang, "clever, alert, wide awake," by 1811, perhaps from fly (n.) on the notion of the insect being hard to catch. Other theories, however, trace it to fledge or flash. Slang use in 1990s might be a revival or a reinvention.

[ Online Etymology Dictionary - "fly" ]

When you come across slang terms whose definition are hard to find, the Urban Dictionary can be a friend. (Just beware the amount of obscenity in it).

fly

cool, in style

He was drivin some fly ass car

I'm so fly

The rapper way of saying that you are way cool

I'm so fly chicks wanna bang me when I drive by

Since definitions in the Urban Dictionary can be written by anyone (and sometimes I think 14-year-old boys write a lot of them), it's safer and more reliable to stick to professional dictionaries for anything other than hard-to-find definitions of slang. I mean, use TUD as a last resort, probably.

This is a slang term that I've heard in the late 80's/early 90's and it means "good looking" or "really good." I believe it was prevalent throughout that time period among the young in the U.S. at least, but is not so much anymore.

Anytime I hear this I think late 80's/early 90's American rap/hip-hop music. This could vary widely by region and not sure if this applies outside the U.S.