Entry 1 sense Webster, 1913 Tartness · Tart·ness · IPA /tˈɑrtnəs/ 01 n. The quality or state of being tart. 1. The quality or state of being tart. Syn. Acrimony; sourness; keenness; poignancy; severity; asperity; acerbity; harshness. See Acrimony.