invasion vs inroad

invasion and inroad both are nouns.

Word	Noun	Adjective	Verb	Adverb
invasion	Yes	No	No	No
inroad	Yes	No	No	No

As nouns, inroad is a hyponym of invasion; that is, inroad is a word with a more specific, narrower meaning than invasion:

invasion: the act of invading; the act of an army that invades for conquest or plunder
inroad: an invasion or hostile attack

invasion (noun)	inroad (noun)
the act of invading; the act of an army that invades for conquest or plunder	an invasion or hostile attack
any entry into an area not previously occupied	an encroachment or intrusion
(pathology) the spread of pathogenic microorganisms or malignant cells to new sites in the body