anacrusisn.

anacrusis (n.)"unstressed syllable at the beginning of a verse," 1833, Latinized from Greek anakrousis "a pushing back," of a ship, "backing water," from anakrouein "to push back, stop short, check," from ana- "back" (see ana-) + krouein "to strike," from PIE *kreue- (2) "to push, strike" (cognates: Russian krusit, Lithuanian krusu "to smash, shatter," Old Church Slavonic kruchu "piece, bit of food," Old English hreowian "feel pain or sorrow," Old Norse hryggja "make sad").