High Quality Content by WIKIPEDIA articles! Siamese twins (also irreversible binomials,binomials,binomial pairs, freezes) in the context of the English language refers to a pair or grouping of words that is 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 sink or swim (two verbs) are various examples of Siamese twins.