http://www.logainm.ie/ga/s?txt=An+fhoithir&str=onIf you click the top two pins on the map it should give you "aill nó aillte" ("cliff or cliffs") as the category of place it is. Or you can scroll down below the map and see the same list of three - though this doesn't always work. Just to add to franc91's post, the link he gave you is to the most authoritative dictionary, which, as he says, gives
foithir as a variant of
fothair. (
Foithir/fothair are the basic forms, which become
fhoithir/fhothair following the def. article
an. There's a
An Fhothair (anglicised as 'Faugher') in Donegal.