keen (adj.) Look up keen at Dictionary.com
c.1200, from Old English cene "bold brave," later "clever, wise," from Proto-Germanic *kan- "be able to" (see can). Original prehistoric senses seem to have been both "brave" and "skilled;" cognate with Old Norse kænn "skillful, wise," Middle Dutch coene "bold," Dutch koen, Old High German kuon "pugnacious, strong," German kühn "bold, daring." Sense of "eager" is from mid-14c. The meaning "sharp" is peculiar to English: of blades and edges early 13c., of sounds c.1400, of eyesight c.1720. A popular word of approval in teenager and student slang from c.1900.
keen (v.) Look up keen at Dictionary.com
"lament," 1811, from Irish caoinim "I weep, wail, lament," from Old Irish coinim "I wail." Related: Keened; keening. As a noun from 1830.