The Collaborative International Dictionary of English v.0.48:
Armet \Arm"et\, n. [F., dim. of arme arm, or corrupted for healmet helmet.] A kind of helmet worn in the 14th, 15th, and 16th centuries. [1913 Webster]WordNet (r) 3.0 (2006):
armet n 1: a medieval helmet with a visor and a neck guard