The Collaborative International Dictionary of English v.0.48:
Seaboat \Sea"boat`\ [AS. s[=ae]b[=a]t.] 1. A boat or vessel adapted to the open sea; hence, a vessel considered with reference to her power of resisting a storm, or maintaining herself in a heavy sea; as, a good sea boat. [1913 Webster] 2. (Zool.) A chiton. [1913 Webster]