smarten definition
Definition of smarten up. 1 US : to become more intelligent or aware : to become smarter He'd better smarten up or he'll get fired. 2 US : to make (someone or something) smarter or more aware Someone needs to smarten him up before he gets in trouble. 3 : to make (someone or something) neat and attractive They smartened themselves up for the party. They smartened up the room for the party.