A male seal. The word is not in Ogilvie, and the Century Dict. gives no example.
1830. On it [the island] reposed, in great state, an old wig (the male seal.) Some of our men boarded the island, and pelted his wigship with pieces of ice, till he was compelled to abdicate . These old wigs are more than twice as large as the female seal and might be mistaken for another species of animals . I had never seen an old wig on shore, consequently knew but little about them, but having killed a good many seals and one sea-elephant, I thought myself a match for a wig.N. Ames, A Mariners Sketches, pp. 136, 145, 146. [Other examples also.]