Siamese twins (linguistics)

Siamese twins (also irreversible binomials,binomials,binomial pairs, nonreversible word pairs, or freezes) in the context of the English language refer to a pair or group of words used together as an idiomatic expression or collocation, usually conjoined by the words and or or. The order of elements cannot be reversed. The expressions hammer and sickle (two nouns), short and sweet (two adjectives), and do or die (two verbs) are various examples of Siamese twins.

Many Siamese twins are "catchy" (and thus clichés and catchphrases) due to alliteration, rhyming, or their ubiquity in society and culture. Word combinations like rock and roll, the birds and the bees, mix and match, and wear and tear have become so widely used that their meanings surpass the meaning of the constituent words and are thus inseparable and permanent parts of the English lexicon; the former two are idioms, whilst the latter two are collocations. Ubiquitous collocations like loud and clear and life or death are fixed expressions, making them a standard part of the vocabulary of native English speakers.

Some English words are known to have become obsolete in general but are still found exclusively in an irreversible binomial. In the passage of time since spick and span was coined, the origin and meaning of the word spick has been utterly forgotten; it has become a fossil word that never appears outside the familiar phrase. In other cases an English word (like vim in vim and vigor or abet in aid and abet) will be found more often in such phrases than on its own; such a word may be archaic apart from the collocation.

Certain Siamese twins are known for their use in legalese. Due to the use of precedent in common law, many lawyers use the same collocations found in documents centuries old. So rather than a person "enunciating" a "narrative" or recollecting about a situation, a legal brief will instead declare that a person deposes and says something pertinent. Likewise, a person who bequeaths property habitually writes of his heirs and successors and not some alternative construct.

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