ˈärsə̇s, ˈȧs- noun
( plural ar·ses -ˌsēz)
Etymology: Late Latin & Greek; Late Latin, accented syllable of a metrical foot, from Greek, unaccented syllable of a metrical foot, lifting of the foot in beating time, irregular from aeirein to lift + -sis — more at aorta
1.
a. : the lighter or shorter part of a poetic foot especially in quantitative verse
b. : the accented or longer part of a poetic foot especially in accentual verse
2. : the weak or unaccented part of a musical measure : upbeat — compare thesis