n. [ From Arsenic. ] (Chem.) A compound of arsenic and hydrogen, AsH3, a colorless and exceedingly poisonous gas, having an odor like garlic; arseniureted hydrogen. [ 1913 Webster ]

‖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 ]

☞ 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 ]