Merriam-Webster's Collegiate® Dictionary, 11th Edition
KEEN
I. adjective
Etymology: Middle English kene brave, sharp, from Old English cēne brave; akin to Old High German kuoni brave
Date: 13th century
1. having a fine edge or point ; sharp , affecting one as if by cutting , pungent to the sense ,
2. a. showing a quick and ardent responsiveness ; enthusiastic , eager , intense ,
3. intellectually alert ; having or characteristic of a quick penetrating mind , sharply contested , extremely sensitive in perception , wonderful , excellent , see: sharp keenly adverb keenness noun
II. noun
Date: 1830
a lamentation for the dead uttered in a loud wailing voice or sometimes in a wordless cry,
III. verb
Etymology: Irish caoinim I lament, weep
Date: 1845
intransitive verb
1. to lament with a keen, to make a sound suggestive of a keen, to lament, mourn, or complain loudly, transitive verb to utter by keening, keener noun