ARSIS

noun

1. The stronger part of a musical measure: the part containing the beat.
2. The stronger part of a metrical foot: the part containing the long (heavy) syllable in quantitative meter, or the stressed syllable in a qualitative meter.
3. 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 the thesis.