anacrusis
Concise Oxford English Dictionary © 2008 Oxford University Press:
anacrusis /ˌanəˈkruːsɪs/
▶noun (pl. anacruses /-siːz/) Prosody one or more unstressed syllables at the beginning of a verse.
– origin C19: mod. L., from Gk anakrousis ‘prelude’, from ana- ‘up’ + krousis ‘striking’.
'anacrusis' also found in these Oxford entries:

