The Collaborative International Dictionary
Spencer mast
Spencer \Spen"cer\, n. (Naut.) A fore-and-aft sail, abaft the foremast or the mainmast, hoisted upon a small supplementary mast and set with a gaff and no boom; a trysail carried at the foremast or mainmast; -- named after its inventor, Knight Spencer, of England [1802].
Spencer mast, a small mast just abaft the foremast or
mainmast, for hoisting the spencer.
--R. H. Dana, Jr.