Synonyms for formal

modified

1. Notable for arrangement

   orderly, precise, set, symmetrical; see regular 3.

2. Concerned with etiquette and behavior

   reserved, distant, stiff, ceremonious; see conventional 2, 3, polite 1.

3. Official

   prescribed, confirmed, directed, lawful; see approved, legal 1.

4. In or requiring evening clothes

   full-dress, black tie, white tie, dressy, dressed up, ceremonious, social, in tails and top hat, in one's glad rags*, in a soup and fish*.