arsis
Webster's Dictionary (GCIDE)
Arsis \Ar"sis\ ([aum]r"s[i^]s), n. [L. arsis, Gr. 'a`rsis a raising or lifting, an elevation of the voice, fr. a'i`rein to raise or lift up. Its ordinary use is the result of am early misapprehension; originally and properly it denotes the lifting of the hand in beating time, and hence the unaccented part of the rhythm.]
1.(Pros.) (a) That part of a foot where the ictus is put, or which is distinguished from the rest (known as the thesis) of the foot by a greater stress of voice. --Hermann. (b) That elevation of voice now called metrical accentuation, or the rhythmic accent. [1913 Webster]
Note: It is uncertain whether the arsis originally consisted in a higher musical tone, greater volume, or longer duration of sound, or in all combined. [1913 Webster]
2.(Mus.) The elevation of the hand, or that part of the bar at which it is raised, in beating time; the weak or unaccented part of the bar; -- opposed to thesis. --Moore. [1913 Webster]