spoo‧ner‧is‧m /ˈspuːnərɪzəm/ noun [countable]
[Date: 1900-2000; Origin: William Spooner (1844-1930), British university teacher who supposedly often made such mistakes]
a phrase in which the speaker accidentally exchanges the first sounds of two words, with a funny result, for example ‘sew you to a sheet’ instead of ‘show you to a seat’

[TahlilGaran] Dictionary of Contemporary English ▲