The single-word/multi-word distinction involves what is most plausibly a difference in terminal elements among items of the same category type (e.g. adjective phrases).
Source: wiktionary
Multi-word
Synonyms for "multi-word"
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Sample sentences
2 total sentences available.
The verb categories included two-word multi-word verbs, though terms of more than two words were placed in the phrase category.
Source: wiktionary