The following three surnames are all a little puzzling.
Trevan looks like a classic trev- name, but it isn’t. There’s a place called Trevan at Probus. However, this was originally Tolvan (from tal and ban, meaning brow of a hill). That placename also occurred at Constantine, Illogan and St Hilary in west Cornwall. In those places the name remained Tolvan or Tolvaddon (a later pronunciation).
Yet, while the surname Tolvan was present at Constantine in the 1500s and 1600s it then disappeared. The spelling Trevan or Trevane eventually popped up, although not until the eighteenth century, in south-east Cornwall, between Liskeard and Saltash. It then dispersed fairly widely across east Cornwall and into Devon. It’s more likely therefore that the origin of the surname is the place called Talvans, spelt Tolvan in 1748, at Landrake near Saltash.
Trevellick is a surname associated with the isles of Scilly since at least the 1700s. But did it origjnate there? Unfortunately, early records for Scilly are sparse. But there is no placename Trevellick there. In contrast there are several Trevillicks or Trevallacks, most first spelt as Trevelek, in Cornwall, from St Keverne in the west to Tintagel in the east. The meaning is probably Eleck’s farmstead. The surname was found in mid-Cornwall and on the Lizard in the 1500s but it then vanished. Had it been taken from the Roseland or the Lizard to Scilly in the period before the mid-1600s, where, in contrast, it flourished?
The origin and meaning of Trewavas is more certain. The surname arose from placenames at Breage and Wendron in west Cornwall that mean farm of the winter-dwelling, or winter farm. The surname stayed in that district in the 1500s and early 1600s but then migrated to West Penwith. Dying out in the Carnmenellis district, it established itself mainly at Mousehole, where it grew as the fishing industry expanded in the 1700s and 1800s.