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- [..]

The comic (and usually unintentional) transposition of two initial consonants or other sounds. For example, saying "the queer old dean" when one means to say, "the dear old [..]

The term Spoonerisms originates from the Reverend Spooner, who is well known in England because of a speech problem he is supposed to have had; it is said that he used to mix up the first couple of le [..]

A slip of the tongue where the initial sounds of a pair of words are transposed. Generally used for humour, for example 'a blushing crow'.

(n) transposition of initial consonants in a pair of words

A category of speech error which involves the swapping of components of the syllable between two words. Example: crooks and nannies for nooks and crannies. The error is named after the Reverend Willia [..]

the interchange of the initial letters of two words, usually as a slip of the tongue. "I think I'll go outside and get a freth of bresh air."

Words or phrases in which initial letters or syllables are switched. This often happens accidently as 'slips of the tongue' or a deliberate play on words. When used deliberately, a spoonerism is a figure of speech.

a slip of the tongue where the first 2 letters of 2 successive words are transposed. [W. A. Spooner (1844-1930), British academic noted for slips of this kind]

A play on words on a phrase in which the initial (usually consonantal) sounds of two or more of the main words are transposed. ''The spoonerism "The queer old dean" (instead of "the dear old Queen [..]