spoonerism (n.)

1900, but according to OED in use at Oxford as early as 1885, involuntary transposition of sounds in two or more words (such as "shoving leopard" for "loving shepherd," "half-warmed fish" for "half-formed wish," "beery work speaking to empty wenches," etc.), in reference to the Rev. William A. Spooner (1844-1930), warden of New College, Oxford, who was noted for such disfigures of speech. A different thing from malapropism.