A spoonerism is a mistake made by a speaker in which the first sounds of two words are changed over, often with a humorous result, for example when someone says 'wrong load' instead of 'long road'.
spoonerism in British English
(ˈspuːnəˌrɪzəm)
noun
the transposition of the initial consonants or consonant clusters of a pair of words, often resulting in an amusing ambiguity of meaning, such as hush my brat for brush my hat
Word origin
C20: named after W. A. Spooner (1844–1930), English clergyman renowned for slips of this kind
spoonerism in American English
(ˈspunərˌɪzəm)
noun
an unintentional interchange of sounds, usually initial sounds, in two or more words (Ex.: “a well-boiled icicle” for “a well-oiled bicycle”)
Word origin
after Rev. W. A. Spooner (1844-1930), of New College, Oxford, famous for such slips