The fourth letter represented as <f>; <v> & <u> is a <v>. This is a difficulty, since it could be the final letter of the element <trev> 'farmstead' or the first letter (mutated) of the second element, following <tre>. There are consequently several hypothesis as to the etymology:
1. <trev> 'farmstead' + <ranow> possibly 'frogs'. cf. Breton <ran> 'frog'
2. <tre> 'farmstead' + <branow> 'crows', but note the normal plural is <brini> so this is unlikely.
3. <tre> 'farmstead' + <branow> personal name. N.B. <bran> is an element found in OC personal names. The <-ow> suffix when used with a name indicates "followers of / family of" - the equivalent of <-ing> on OWS.
The latter of these 3 possible derivations is considered the most likely.