formal adj.
1 very correct/official
VERBS be, seem, sound | become
ADV. extremely, very | strictly Learning was by rote and strictly formal. | almost The greeting was polite, almost formal. | fairly, quite, rather, relatively | oddly Her words sounded oddly formal. | stiffly His manner was stiffly formal.
2 concerned with the way sth is done
VERBS be
ADV. merely, purely Getting approval for the plan is a purely formal matter: nobody will seriously oppose it. | largely The monarch retains largely formal duties.
You can also check other dicts: formal (English, 中文解释 ), wordnet sense, Collins Definition