Multiword entry typology
Multiword entries (MWEs), which correspond to multi-word expressions, fall into various types, which don't exactly correspond to Wiktionary categories. This is an attempt to clarify that relationship and to determine whether there ought be some categorization of such entries. The discussion will focus on English.
Multiword entries and PoS headings and categories
Multiword entries can appear under many PoS headings used in Wiktionary: Proverb, Phrase, Idiom (not English?), Noun, Verb, Adjective, Adverb, Preposition. But even Category:English conjunctions has several. The grammatical appropriateness of such categories is subject to challenge, as in CGEL on phrasal verbs, phrasal prepositions, and others.
Main entries, lemmas, alternative forms, and snowclones
MWEs can form a challenge in determining the appropriate main entry, forming a lemma, and determining alternative forms. An MWE that has only one constituent that inflects is not difficult, but some have multiple terms that inflect or allow other variation (multiple or zero articles, determiners, and conjunctions; contractions; synonyms, antonyms; negation). Humorous and creative variations are not uncommon. Some multiword expressions are called snowclones.
Multiword entries and collocations
"Collocations" is a term intended to include idioms but also include other constituents. Some definitions of collocations remove the requirement that the collocation forms a constituent.