"My own village - Lynmouth, north of the above - is the mouth of the river Lyn/e, or from the Gaelic derivation "river river-mouth"

MInd "Llyn" is also a P-Celtic word and (according to Godfrey Watson in his book 'Northumberland Place Names')the old Anglo-Saxon word "hlynn" means a torrent of any kind.

Just because something could be of Gaelic origin it doesn't mean it was. There is a Lynmouth in Devon too which presumably isn't derived from Gaelic. Why look for a Gaelic origin to the word when the local languages had the same/similar possible sources?