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" (source also of Russian krusit, Lithuanian krušu, krušti "to smash, shatter," Old Church Slavonic kruchu "piece, bit of food," Old English hreowian "feel pain or sorrow," Old Norse hryggja "make sad"). Related: Anacrustic.