A spoonerism is a play on words in which corresponding consonants, vowels, or morphemes are switched (see metathesis). It is named after the Reverend William Archibald Spooner (1844–1930), Warden of New College, Oxford, who was notoriously prone to this tendency.
While spoonerisms are commonly heard as slips of the tongue (sometimes spoonerised as tips of the slung), they are considered a form of pun when used purposely as a play on words.