Onset rhymes with:
ansett, inset, sunset, amagansett, ansett, asset, avocet, backset, exocet, handset, headset, heavyset, inset, mediaset, mindset, morrisett, outset, somerset, subset, sunset, typeset, videocassette
Onset sounds like:
ohnstad, onsite, onstad, onstott, ounsted