na-adjective, noun
Describes a person of deep insight and sound judgment, often with a nuance of moral clarity. More formal and literary than 賢い (かしこい).
彼は聡明な判断でチームを救った。
He saved the team with his wise decision.
聡明な人ほど、自分の限界を知っている
The wiser a person is, the more they know their own limits.
賢い is the common everyday word for 'smart' or 'clever'. 聡明 is more formal and implies depth of wisdom and judgment, not just quick thinking.
利口 often means 'clever' or 'well-behaved' in a practical sense, sometimes with a nuance of shrewdness. 聡明 carries a loftier, more intellectual and moral connotation.
From Chinese 聰明／聪明 (cōngmíng). The kanji 聡 (or 聰) means 'keen of hearing' and 明 means 'bright', together suggesting perceptiveness and clarity of mind.