Is the word faint a verb?

Yes, the Word 'faint' is a verb (faint, faints, fainting, fainted), a Word for the act of fainting, an action verb.

The Word 'faint' is also an adjective (faint, fainter, faintest) that describes a lessening of consciousness or intensity, barely discernible; and a noun, a Word for the loss of consciousness due to lack of blood to the brain.