tart (adj.) Look up tart at Dictionary.com
"having a sharp taste," late 14c., perhaps from O.E. teart "painful, sharp, severe" (in ref. to punishment, pain, suffering), of unknown origin; possibly related to the root of teran "to tear." Fig. use, with ref. to words, speech, etc., is attested from c.1600.
tart (n.1) Look up tart at Dictionary.com
"small pie," c.1400, from O.Fr. tarte "flat, open-topped pastry" (13c.), 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.).
tart (n.2) Look up tart at Dictionary.com
"prostitute," 1887, from earlier use as a term of endearment to a girl or woman (1864), sometimes said to be a shortening of sweetheart. But another theory traces it to jam-tart (see tart (n.1)), which was British slang early 19c. for "attractive woman." To tart (something) up is from 1938.