1540s, "hostile incursion, raid, foray," from in- (2) "in;" second element is road (n.) in the obsolete sense of "riding;" related to raid (v.). Related: Inroads.
they made inroads in the United States market
inquiry
inquisition
inquisitive
inquisitor
inro
inroad
insalubrious
insane
insanity
insatiability
insatiable
