su·shi 
(s
sh
ē)
n. Cold cooked rice dressed with vinegar that is shaped into pieces and topped with raw or cooked fish, or formed into a roll with fish, egg, or vegetables and often wrapped in seaweed.
[Japanese, from Old Japanese susi, salted fish preserved in fermenting rice, possibly a nominalization of susi, sour : su-, sour (akin to su, vinegar, perhaps imitative of a puckering or sucking sound, or from Early Middle Chinese tshɔh, vinegar) + -si, finite predicative adjective ending.]

sushi