dilator

noun

di·​la·​tor (ˈ)dī-ˈlāt-ər, də- 

: 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