Английский Этимологический словарь - tart (n.)

- "small pie," 14c., from O.Fr. tarte, possibly an alteration of torte, from L.L. torta "round loaf of bread" (in M.L. "a cake, tart"), infl. in M.E. by tart (adj.). The meaning "prostitute" is found 1887, from earlier use as a term of endearment (1864), sometimes said to be a shortening of sweetheart. But another theory traces it to jam-tart, British slang early 19c. for "attractive woman." To tart (something) up is from 1938.