A spoonerism is an occurrence of speech in which corresponding consonants, vowels, or morphemes are switched (see metathesis) between two words of a phrase. These are named after the Oxford don and priest William Archibald Spooner, who reportedly commonly spoke in this way.

Examples include saying "blushing crow" instead of "crushing blow", or "runny babbit" instead of "bunny rabbit". While spoonerisms are commonly heard as slips of the tongue, they can also be used intentionally as a word play. Since the rise of the Internet and wordfilters, spoonerisms have also become deliberately used as filter-avoidance spellings of filtered terms.

The first known spoonerisms were published by the 16th-century author François Rabelais and termed contrepèteries. In his novel Pantagruel, he wrote "femme folle à la messe et femme molle à la fesse" ("insane woman at Mass, woman with flabby buttocks").

Spoonerisms are named for the Reverend William Archibald Spooner (1844–1930), Warden from 1903 to 1924 of New College, Oxford, who was allegedly susceptible to this mistake. The Oxford English Dictionary records the word spoonerism as early as 1900. The term was well-established by 1921. An article in The Times from that year reports that:

The boys of Aldro School, Eastbourne, ... have been set the following task for the holidays: Discover and write down something about: The Old Lady of Threadneedle-street, a Spoonerism, a Busman's Holiday...

An article in the Daily Herald in 1928 reported spoonerisms to be a "legend". In that piece, Robert Seton, once a student of Spooner's, claimed that Spooner:

...made, to my knowledge, only one "Spoonerism" in his life, in 1879, when he stood in the pulpit and announced the hymn: 'Kinkering Kongs their Titles Take' ["Conquering Kings their Titles Take"]...Later, a friend and myself brought out a book of "spoonerisms".

In 1937, The Times quoted a detective describing a man as "a bricklabourer's layer" and used "Police Court Spoonerism" as the headline.