早速
さっそく · sassoku · JLPT N2 · adverb
at once
早 (early) + 速 (speed): done with early speed, so right away
早速 = 早い (early) + 速い (quick). Something done early and fast happens at once. Sounds like 'sass-o-ku', a quick sassy snap.
早 — sun 日 + ten 十 (originally 甲, a helmet/sprout)
Originally depicted the sun 日 rising above a sprouting plant or a person's head, suggesting the early morning when the sun first appears. The lower component was simplified over time into 十. The core meaning 'morning, early' has remained stable since oracle bone script.