1. Sharp, keen refer to the edge or point of an instrument, tool, and the like. Sharp applies, in general, to a cutting edge or a point capable of piercing: a sharp knife; a sharp point. Keen is usually applied to sharp edges: a keen sword blade. 6. clear. 8. acrid, bitter, piquant, sour. 10. piercing, nipping, biting. 11. severe, excruciating. 12. unmerciful, cutting, acid, acrimonious, pointed, biting. 16. attentive. 17. clever, discriminating, discerning, perspicacious. As applied to mental qualities, sharp, keen, intelligent, quick have varying implications. Sharp suggests an acute, sensitive, alert, penetrating quality: a sharp mind. Keen implies observant, incisive, and vigorous: a keen intellect. Intelligent means not only acute, alert, and active, but also able to reason and understand: an intelligent reader. Quick suggests lively and rapid comprehension, prompt response to instruction, and the like: quick at figures. 20. shady, deceitful.