shamus n.

"police officer, detective," 1920, apparently first in "The Shamus," a detective story published that year by Harry J. Loose (1880-1943), a Chicago police detective and crime writer; the book was marketed as "a true tale of thiefdom and an expose of the real system in crime." The word is said to be probably from Yiddish shames, literally "sexton of a synagogue" (according to Israel Zangwill "a potent personage only next in influence to the President"), from Hebrew shamash "servant." Probably influenced by Celtic Seamus "James," as a typical name for an Irish cop.