WordNet sense 1 (having or demonstrating ability to recognize or draw fine distinctions):

acute, discriminating, incisive, keen, penetrating, penetrative, piercing

WordNet sense 2 (having the ability to perceive or understand; keen in discernment):

perceptive

WordNet sense 3 (as physically painful as if caused by a sharp instrument):

cutting, stabbing, lancinate, lancinating

WordNet sense 4 (keenly and painfully felt; as if caused by a sharp edge or point):

sharp

WordNet sense 5 (easy to perceive; especially clearly outlined):

distinct