The Collaborative International Dictionary of English v.0.48:

Inroad \In"road`\ ([i^]n"r[=o]d`), n.
   The entrance of an enemy into a country with purposes of
   hostility; a sudden or desultory incursion or invasion; raid;
   encroachment.
   [1913 Webster]

         The loss of Shrewsbury exposed all North Wales to the
         daily inroads of the enemy.              --Clarendon.
   [1913 Webster]

         With perpetual inroads to alarm,
         Though inaccessible, his fatal throne.   --Milton.

   Syn: Invasion; incursion; irruption. See Invasion.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Inroad \In*road"\ ([i^]n*r[=o]d"), v. t. [imp. & p. p.
   Inroaded; p. pr. & vb. n. Inroading.]
   To make an inroad into; to invade. [Obs.]
   [1913 Webster]

         The Saracens . . . conquered Spain, inroaded Aquitaine.
                                                  --Fuller.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inroad
    n 1: an encroachment or intrusion; "they made inroads in the
         United States market"
    2: an invasion or hostile attack

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "inroad":
   advances, air attack, air raid, air strike, attack, bankruptcy,
   boarding, breakage, breakdown, breakthrough, collapse, crack-up,
   crippling, damage, destruction, detriment, dilapidation,
   disablement, disrepair, encroachment, entrance, entrenchment,
   escalade, fire raid, foray, harm, hobbling, hurt, hurting,
   impairment, impingement, imposition, incapacitation, incursion,
   infiltration, influx, infraction, infringement, injection, injury,
   insinuation, interference, interjection, interloping,
   interposition, interposure, interruption, intervention, intrusion,
   invasion, irruption, loss, maiming, mayhem, mischief, mutilation,
   obtrusion, overrun, overstepping, overswarm, penetration, progress,
   raid, razzia, ruination, ruinousness, sabotage, saturation raid,
   scaling, scathe, shuttle raid, sickening, spoiling, transgression,
   trespass, trespassing, unlawful entry, usurpation, weakening