首音互换或首音误置（spoonerism）原指将英文词汇中的两个字词之元音、辅音或语素调换之现象，例如将「The Lord is a loving shepherd」（主乃慈爱之牧）中「loving」与「shepherd」的声母（「l」及「sh」）调换，念成「The Lord is a shoving leopard」（主乃推撞之豹）。首音误置可以是故意玩弄文本之举，亦可以是无意中产生的错误，常会产生意想不到的诙谐效果。

类似spoonerism的首音误置现象除在英文出现外，于世上不少语言亦会发生。

A spoonerism is an error in speech or deliberate play on words in which corresponding consonants, vowels, or morphemes are switched (see metathesis) between two words in a phrase.

An example is saying "The Lord is a shoving leopard" instead of "The Lord is a loving shepherd." While spoonerisms are commonly heard as slips of the tongue resulting from unintentionally getting one's words in a tangle, they can also be used intentionally as a play on words.