Multiword

Multiword refers to sequences of two or more words that function as a single unit within a language. In linguistic and natural language processing contexts, this concept is most often discussed under the heading of multiword expressions (MWEs). MWEs encompass a wide range of word combinations, including idioms, phrasal verbs, fixed collocations, and compound nouns. Many MWEs have meanings or usages that cannot be reliably inferred from their individual components, though some are more transparent or compositional.

Common subtypes include idioms, where the whole expression has a figurative meaning (for example, kick the bucket meaning to die); phrasal verbs, where a verb combines with a particle or preposition to yield a distinct meaning (look up, break down); collocations, which are habitual word pairings with strong co-occurrence tendencies (strong tea, heavy rain); and compound nouns or proper names (New York, coffee table). Light-verb constructions, such as take a walk or make a decision, are another often discussed category. MWEs can be fixed or semi-fixed, and they may vary in their degree of syntactic flexibility.

MWEs pose particular challenges for language technologies. They can affect tokenization, parsing, machine translation, and information retrieval, especially when their meanings are non-literal or when they translate poorly across languages. Detection and treatment of MWEs rely on linguistic analysis, statistical methods, and, increasingly, neural models, often aided by specialized lexicons and annotated corpora. Cross-linguistic variation means MWEs behave differently across languages, requiring language-specific resources and approaches.