(baseball, of the ball) While in the air, without having touched the ground. / (idiomatic) Spontaneously or extemporaneously; done as one goes, or during another activity.

Alternative spelling of on the fly

(zoology) Any insect of the order Diptera; characterized by having two wings (except for some wingless species), also called true flies.

(intransitive) To travel through the air, another gas, or a vacuum, without being in contact with a grounded surface. / (transitive, intransitive, archaic, poetic) To flee, to escape (from).

(obsolete) The action of flying; flight. / An act of flying. / (baseball) A fly ball. / (American football) Short for fly route. / A piece of canvas that covers the opening at the front of a tent.

(intransitive, baseball) To hit a fly ball; to hit a fly ball that is caught for an out. Compare ground (verb) and line (verb).

(slang, dated) Quick-witted, alert, mentally sharp. / (slang) Well dressed, smart in appearance; in style, cool. / (slang) Beautiful; displaying physical beauty.

(rural, Scotland, Northern England) A wing.

That flies or can fly. / Brief or hurried. / Capable of speed / (nautical, of a sail) Not secured by yards. / (nautical, of a vessel) Capable of foiling.

present participle of fly