v. phr. 1. To let or make steam escape; send out steam. The janitor let off some steam because the pressure was too high. 2. informal To get rid of physical energy or strong feeling through activity; talk or be very active physically after forced quiet. After the long ride on the bus, the children let off steam with a race to the lake. When the rain stopped, the boys let off steam with a ball game. Bill's mother was very angry when he was late in coming home, and let off steam by walking around and around. Bill had to take his foreman's rough criticisms all day and he would blow off steam at home by scolding the children.
Compare: BLOW ONE'S TOP, LET GO 6 .