/ahr"sis/ , n. , pl. arses /-seez/ .
1. Music. the upward stroke in conducting; upbeat. Cf. thesis (def. 4).
2. Pros.
a. the part of a metrical foot that bears the ictus or stress.
b. (less commonly) a part of a metrical foot that does not bear the ictus. Cf. thesis (def. 5).
[ 1350-1400; ME: raising the voice ar- (s. of aírein to raise, lift) + -sis -SIS ]