A spoonerism is a slip of the tongue where you swap the first sounds of two words in a phrase, and the result comes out funny. If you mean to say 'a well-oiled bicycle' and it comes out 'a well-boiled icicle', that is a spoonerism. The classic examples all follow the same shape: take the sound at the start of one word, take the sound at the start of a nearby word, and trade them. 'You have wasted two terms' becomes 'you have tasted two worms'. 'Show you to a seat' becomes 'sew you to a sheet'. The word is named after a real man, Reverend William Spooner, an Oxford teacher who was famous for making these mistakes — though people say most of the famous ones were made up later by students who enjoyed the joke too much to stop. Two things to notice about how the word is used. First, a true spoonerism is an accident, a mistake the mouth makes when it is running faster than the brain. Second, and this is where people stretch it: nowadays we also call it a spoonerism when someone swaps the sounds on purpose, for a joke, or in a name for a shop or a band. Purists will tell you that on-purpose ones don't count. Most people use the word for both anyway. It is a slightly bookish word — you meet it in language classes, in newspaper columns about funny English, in puzzle books — not something you would hear in ordinary conversation. It is a countable noun: one spoonerism, several spoonerisms.

首音互換（斯普納症、斯普納式口誤）。中文沒有真正對應的詞，因為這種錯誤靠的是英文字首的子音；台灣課堂上通常就直接說「首音互換」或講解「把兩個字的第一個音對調」。跟「口誤」不完全一樣——口誤是任何說錯，首音互換是特定的那一種對調。