Webster's Revised Unabridged Dictionary · 1913

Keen

Keen (kēn) , adjective

[Old English kene sharp, bold, Anglo-Saxon cēne bold; akin to Dutch koen, Old High German kuoni, German kuhn, OSw. kyn, kon, Icelandic kann, for konn wise; perh. akin to English ken, can to be able. r45.]

1.
Sharp; having a fine edge or point; as, a keen razor, or a razor with a keen edge.
A bow he bare and arwes [arrows] bright and kene. — Chaucer
That my keen knife see not the wound it makes. — Shakespeare
2.
Acute of mind; sharp; penetrating; having or expressing mental acuteness; as, a man of keen understanding; a keen look; keen features.
To make our wits more keen. — Shakespeare
Before the keen inquiry of her thought. — Cowper
3.
Bitter; piercing; acrimonious; cutting; stinging; severe; as, keen satire or sarcasm.
Good father cardinal, cry thou amen To my keen curses. — Shakespeare
4.
Piercing; penetrating; cutting; sharp; -- applied to cold, wind, etc.; as, a keen wind; the cold is very keen.
Breasts the keen air, and carols as he goes. — Goldsmith
5.
Eager; vehement; fierce; as, a keen appetite.
Of full kene will. — Piers Plowman
So keen and greedy to confound a man. — Shakespeare
6.
Wonderful; delightful; marvelous; as, that would be keen. [slang]

Keen is often used in the composition of words, most of which are of obvious signification; as, keen-edged, keen-eyed, keen-sighted, keen-witted, etc.

Keen , transitive verb

To sharpen; to make cold. [Rare]
Cold winter keens the brightening flood. — Thomson

Keen , noun

[Ir. caoine.]

A prolonged wail for a deceased person. Compare Coranach. [Ireland] — Froude

Keen , intransitive verb

To wail as a keener does. [Ireland]