Solution

FORMAL

4 clues

Black-tie

Word class: Common adjective
Nature of clue: Description
Difficulty: Easy
Topics: Fashion, Traditions

Dressy

Word class: Common adjective
Nature of clue: Synonym
Difficulty: Very easy
Topics: Fashion

Official

Word class: Common adjective
Nature of clue: Synonym
Difficulty: Very easy

Proper

Word class: Common adjective
Nature of clue: Synonym
Difficulty: Medium

Other solutions to Proper

Words are categorized by artificial intelligence: there can be mistakes.