Entry 2 senses · 2 variants Webster, 1913 Mastless · Mast·less · IPA /ˈmæstləs/ a. a. 01 a. Bearing no mast; as, a mastless oak or beech. 1. Bearing no mast; as, a mastless oak or beech. 02 a. Having no mast; as, a mastless vessel. 1. Having no mast; as, a mastless vessel.