finely sharpened, as an edge; so shaped as to cut or pierce substances readily

a keen razor.

sharp, piercing, or biting

a keen wind; keen satire.

characterized by strength and distinctness of perception; extremely sensitive or responsive

keen eyes; keen ears.

having or showing great mental penetration or acumen

keen reasoning; a keen mind.

animated by or showing strong feeling or desire

keen competition.

intense, as feeling or desire

keen ambition; keen jealousy.

eager; interested; enthusiastic (often fol. by about, on, etc., or an infinitive)

She is really keen on going swimming.

Slang . great; wonderful; marvelous.

noun

sharpness , shrewdness , acumen , judgment , acuteness , intelligence , bite , incisiveness , sting , astuteness , clear-sightedness , discrimination , eye , nose , penetration , perceptiveness , percipience , percipiency , perspicacity , sagacity , sageness , wit