臺灣現代流行的一個語詞「小三」，這個外遇對象多半指的是女性，後來又衍生出相對應的男性稱呼「小王」。其實閩、客族群早期已經有其相對應的稱呼，閩南族群稱之為「契兄」，客家族群稱之為「契哥」。這個「契」表示契約之義，但後來大家都理解成「客兄」或「客哥」。本論文分成三個部份討論。首先分別就文獻材料討論閩南語「契兄」和客家話「契哥」的語義發展，由早期表達情人意義，後來轉變成指外遇對象。其次討論「契兄」和「契哥」分別變成「客兄」和「客哥」的文字誤用及其影響因素。最後述及在時代競爭之下，閩南語「契兄」這個語詞將會繼續保存，而客家話「契哥」則逐漸走入歷史。

In Taiwan, a mistress is referred to as "Xiao San" in popular culture. An equivalent for a male lover in an affair is "Xiao Wang". The Southern Min people have the correspondent word kheʔ hiã and the Hakka kheʔ ko. There are three parts in this paper. First, we discuss the semantic grammaticalization of these two words respectively by corpora. Their meanings change from ‘the beloved one’ to a lover in an affair. Second, we talk about the misuse of Chinese characters to which there are three possible reasons: folk writing, mass communication system, and the conflict between the Southern Min people and the Hakka. Last, we predict the Southern Min word will survive and the Hakka word will eliminate.