A hawk is a bird of prey which feeds on the flesh of other animals.
A hawk in political terminology is someone who favors war, or a strong military, or participation in a particular war. Often it is used as an adjective rather than a noun, as in "hawkish". It is in contrast with a dove, who advocates peace instead.
Before the War of 1812 was declared, those Congressmen, such as Henry Clay who called for war against Britain were called "war hawks."