Chiefly U.S. colloquial. Of or characteristic of refined or high-class people; of superior quality; stylish, tasteful; (in negative sense)…

like or characteristic of a ‘toff’, stylish.

Having a high or fashionable tone; high-toned, stylish; ‘swell’.

In occasional uses: having ‘style’ (in various senses: see style, n. 14 23).

U.S. Chiefly Black English. Attractive, good-looking; hence, excellent, fabulous (cf. fly boy n. at additions below; fly girl, n.).

Chiefly among rap musicians and enthusiasts: excellent, great, impressive.