Planning a trip to Huddersfield the other day, I happened across the nearby villages of *Linthwaite* ([pronounced *lin-fit*](http://www.hintsandthings.co.uk/library/Place-name-pronunciation.htm)) and Slaithwaite ([pronounced *slow-it, or slaw-it*](http://www.hintsandthings.co.uk/library/Place-name-pronunciation.htm) depending who you ask). Thinking this strange I looked into the matter and turned up *Seathwaite* ([pronounced *sea-wait*](http://users.tinyworld.co.uk/peterostle/friends.html)), and also [*Bassenthwaite*](http://dictionary.reference.com/browse/bassenthwaite) and [*Hawthornthwaite*](http://www.pronouncenames.com/pronounce/hawthornthwaite), pronounced as you would expect. I have been unable to turn up any guide as to how *Haverthwaite*, *Hampsthwaite* or *Thornthwaite* are pronounced.

I realise that the pronunication of place names surpasseth all understanding, but my question is, are the three odd pronounciations the remains of an older form? If so, how came their names to be spelt that way? And if not, is there any reason those particular names are corrupted and not others?

I suspect it isn't just a matter of local accent as *Seathwaite* is quite a way from *Slaithwaite* and *Linthwaite* (which are quite close together). Is there perhaps an isogloss for this?