gal·le·ass also gal·li·ass 
(gălē-ăs′, -əs)
(gălē-ăs′, -əs)n.
Nautical
Nautical
A large, fast, heavily armed three-masted Mediterranean galley of the 1500s and 1600s.
[Old French galeasse, from Old Italian galeaza, augmentative of galea, galley, from Old Provençal or Catalan; see GALLEY.]