Translation according to P. W. Joyce:
Cartron is the Anglo-Irish term corresponding with Irish ceathramha, a quarter of land. See vol. i.p. 245 [reproduced below].
In many parts of Ireland the Anglo-Norman settlers introduced terms derived from their own language, and several of these are now very common as townland names. Cartron signifies a quarter, and is derived through the French quarteron from the medieval Lat. quarteronus; it was in very common use in Connaught as well as in Longford, Westmeath, and King's County; and it was applied to a parcel of land varying in amount from 60 to 160 acres. There are about 80 townlands called Cartron, chiefly in Connaught, and 60 others of whose names it forms the beginning. The terms with which it is compounded are generally Irish, such as Cartronganny near Mullingar, Cartron-gainimh, sandy cartron; Cartronnagilta in Cavan, the cartron of the reeds; Cartronrathroe in Mayo, the cartron of the red fort.