Noah Webster's New International Dictionary of the English Language

1. (superl.) Sharp; having a fine edge or point; as, a keen razor, or a razor with a keen edge.

2. (superl.) Acute of mind; sharp; penetrating; having or expressing mental acuteness; as, a man of keen understanding; a keen look; keen features.

3. (superl.) Bitter; piercing; acrimonious; cutting; stinging; severe; as, keen satire or sarcasm.

4. (superl.) Piercing; penetrating; cutting; sharp; -- applied to cold, wind, etc, ; as, a keen wind; the cold is very keen.

5. (superl.) Eager; vehement; fierce; as, a keen appetite.

6. (v. t.) To sharpen; to make cold.

7. (n.) A prolonged wail for a deceased person. Cf. Coranach.

8. (v. i.) To wail as a keener does.