1814 in the cookery sense, agent noun from steam (v.). From 1825 as "a vessel propelled by steam," hence steamer trunk (1885), one that carries the essentials for a voyage.

"Chinese cuisine prepared as bite-sized portions served in small steamer baskets or on small plates," 1948, from Cantonese tim sam (Chinese dianxin) "appetizer," said to mean literally "touch the heart." Ayto ("Diner's Dictionary") gives the elements as tim "dot" + sam "heart."

also show-boat, 1838, "river steamer on which theatrical performances are given," from show (n.) + boat (n.). The verb meaning "to show off" is attested from 1951; the notion is of performing in the overly theatrical style of showboat players.