Green’s Dictionary of Slang

(US) a bartender.

1947		S.C. Adams Jr. personal doc. q. in Adams Thesis in Gordon & Nemerov Lost Delta Found (2005) 256: She asked the bar room tender, has he seen old Albert here .
1994		G. Pelecanos Shoedog 18: [H]e mostly hung out at the marina bars [...] where he became friendly with the wait staff and tenders.