dilator

noun
di·​la·​tor | \ (ˈ)dī-ˈlāt-ər, də- How to pronounce dilator (audio) \

Medical Definition of dilator

: one that dilates: as
a : an instrument for expanding a tube, duct, or cavity a urethral dilator

called also divulsor

b : a muscle that dilates a part
c : a drug (as a vasodilator) causing dilation