The Collaborative International Dictionary of English v.0.48:

Mastless \Mast"less\, a. [See 2d Mast.]
   Having no mast; as, a mastless vessel.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mastless \Mast"less\, a. [See 1st Mast.]
   Bearing no mast; as, a mastless oak or beech. --Dryden.
   [1913 Webster]