onset noun
ADJ. rapid, sudden the sudden onset of the disease | slow | early | delayed, late
VERB + ONSET delay | mark His first hit record marked the onset of an astonishing career.
PREP. after the ~ after the onset of sleep | at the ~ at the onset of the war | before/prior to the ~, since the ~
You can also check other dicts: onset (English, 中文解释 ), wordnet sense, Collins Definition