Bull Moose \Bull Moose\ (U. S. Politics)
   (a) A follower of Theodore Roosevelt in the presidential campaign of 1912; -- a sense said to have originated from a remark made by Roosevelt on a certain occasion that he felt ``like a bull moose.'' [Cant]
   (b) The figure of a bull moose used as the party symbol of the Progressive party in the presidential campaign of 1912. -- Bull Mooser. [Cant]

Source: Webster's Revised Unabridged Dictionary (1913)