Jam1  —v. (-mm-) 1 a (usu. Foll. By into, together, etc.) Squeeze, cram, or wedge into a space. B become wedged. 2 cause (machinery etc.) To become wedged or (of machinery etc.) Become wedged and unworkable. 3 a block (a passage, road, etc.) By crowding etc. B (foll. By in) obstruct the exit of (was jammed in). 4 (usu. Foll. By on) apply (brakes etc.) Forcefully or abruptly. 5 make (a radio transmission) unintelligible by interference. 6 colloq. (in jazz etc.) Improvise with other musicians. —n. 1 squeeze, crush. 2 crowded mass (traffic jam). 3 colloq. Predicament. 4 stoppage (of a machine etc.) Due to jamming. 5 (in full jam session) colloq. (in jazz etc.) Improvised ensemble playing. [imitative]