[TA]Avoid the incorrect term right main stem (or mainstem) bronchus. primary division of the tracheobronchial tree arising as the right of branch at the bifurcation of the trachea; it enters the hilum of the right lung, giving off the superior lobe bronchus and continuing downward to give off the middle and inferior lobe bronchi. It is shorter, of larger caliber, and more nearly vertical than the left main bronchus, thus, aspirated objects more frequently lodge on the right side. SYN: bronchus principalis dexter [TA].