onset

(ŏnˈsĕtˌ, ônˈ-)

1. An onslaught; an assault.
2. A beginning; a start: the onset of a cold.
3. Linguistics The part of a syllable that precedes the nucleus. In the word nucleus (no͞oˈklē-əs), the onset of the first syllable is (n), the onset of the second syllable is (kl), and the last syllable has no onset.