It seems generally accepted (see following references) that the name Gwent evolved from the Romano-British Venta (for example Venta Silurum → Caer Guent → Caerwent [Info]), though its history and meaning are debated.
Williams (quoted in Coates*) suggested it may have meant "field" (tracking from the modern Welsh gwellt "grass"?). From this and other work Gelling* suggests the following evolution: Romano-British Venta "Field" → Welsh Gwent "Field" → "Marketplace"). Coates* holds with the more general "place", suggesting it is a pre-British word, while Ó Máille*, working from the Irish side suggests it means "River".
There seems to be general agreement with the former researchers that the root of the word is a hypothetical term *uentā (See this discussion as well) However, Williams* suggests it is possible it relates (further back?) to another hypothetical Celtic term *Ven which may mean "pleasant" (he suggests this can be seen in the Welsh gwên "smile"). Thus the district might have been somewhere pleasant (not that Gwent isn't!).
Other places containing W/U/Vent include, from Roman Britain: Venta Icenorum (also just Venta*, near Caistor St. Edmund, south of Norwich* [Info]); Venta Belgarum (also just Venta*, in Welsh Caer-went* or Cair Guinntguic*, "Winchester"* [Info]); Glannoventa (Fort east of Ravenglass, Cumbria* [Info]); Bannaventa (Whilton Lodge, Norton, Northamptonshire?* [Info]); from Welsh: Cas-Went ("Chepstow", after the area Gwent); and possibly also: Llinwent* (Near Llanbister?); Arddunwent* (near Mold [Info]); Derguentid* (battle site in the Historia, possibly "Derwent"); Gosgyrnwent* (?); Kilwentford* (?); Teirwent* (?); Ynys Gwent* (?); and Banwen*. Possibly related Continental and Irish placenames can be found in Coates* and Ó Máille*.
All this said, the current county seems extremely likely. Gwent was, very broadly, the area between the Usk and the Wye (Modern Map), essentially matching the current area of Monmouthshire for much of its existance - though this does little justice to the evolution of its boundaries.