The adjective incisive describes something that is sharp, decisive, and direct. A comment that cuts right to the bone can be just as incisive as an actual knife.
The word incisive is rooted in a Latin word that literally means "to cut with a sharp edge." To help you remember the meaning, you can think of the similar word, incisors, which are the teeth that are sharp and cut and tear. The more figurative meaning of describing something that is mentally sharp first appeared in the 1850s. Keen criticism and cutting remarks have been called incisive ever since.