Looks like there are many Frasers in Killearnan who were known by that by-name. Various spellings Uirach, Uirrach, Uarach, Uarrach, dating from 1761 to 1804.
My guess would be they were originally from Urray or Orrin, much like the Hearachs (of Harris) and the Sgitheanachs (of Skye).
Unfortunately the meaning of the name is probably lost in time.
Alasdair