keen, adj. — Green’s Dictionary of Slang

keen adj.

[SE keen, eager or shrewd]

(US) splendid, competent, sharply dressed etc; thus keen society, high society.

1899		Ade Fables in Sl. (1902) 182: It was rumored in Keen Society that they didn’t Belong.
1903		Ade ‘“Buck” and Gertie’ in In Babel 299: He was ‘just as good’ as any of the Chamberlains, living or dead, and possibly a few degrees keener on ordinary topics.
1905		‘Hugh McHugh’ You Can Search Me 11: It’s going to afford me a bunch of keen delight.
1918		‘Max Brand’ ‘Above the Law’ in Coll. Stories (1994) 65: I wish I was keen in the bean.
1929		E. Booth Stealing Through Life 65: I could square it for you. Keen skirt, too.
1936		Cab Calloway ‘My Girl Mezzanine’ 🎵 Have you seen the cute and keen / Baby sweet as a tangerine?
1947		S.J. Perelman ‘How Sharper Than a Serpent’s Tooth’ in Keep It Crisp 141: You wear the keenest threads on the campus.
1956		N. Mitford Noblesse Oblige (1980) 87: I mean slang [...] as opposed to the adoption of modish catch-phrases (e.g. keen, ostentatiously efficient).
1962		Mad mag. Dec. 36: Did you notice that dreamy Carl Klutz [...] and that keen Dick Drab.
1967		M. Braly On the Yard (2002) 65: You’ve got to play it keen, he whispered to himself. Keen. He crooned the word.
1983		R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
2002		Josh Dobbin Itsthecatsass.com 🌐 More importantly, charter members will be able to get discounts on the keen gear that we’ll eventually be selling.

In derivatives

keeno (n.)

one who is seen as overly dedicated to their (school) work by the standards of the mass.

2018

S. Jordison Versopolis 1 Aug. 🌐 [A]t my school, one of the deadliest insults you could hurl at someone was that they were a ‘keeno’, that they actually tried in lessons.