<tre> 'farmstead, settlement' + <Mel> personal name - Mael from <maglos> 'prince'
Historic forms:
Trevael 1327 (Gover, 1948)
Trevael 1380 (Gover, 1948)
Trevail 1334 (Gover, 1948)
Trevail 1768 (of Edward Stevens, Vivian Stevens, Matthew Stevens and William Richards)(*CRO, X110/23, 1768)
Trevail Mill 1777 (of William Stevens)(*CRO, X110/23, 1777)
Treveal 1821 (occupiers are Peter Chaple, Christopher Osborn, William and James Michell, James Quick, William Sandry, James Reyonalds, Nicholas Webb and William Stevens)(*CRO, P255/16b/1, 1821)
Treveal 1842 (CRO, TA/255, 1842)
Treveal 1884 (farm)(Symons, 1884)