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Iddon (pronounced ithon (th as in the, not think) is a Welsh name, derived from iud 'lord' + on (diminutive ending). Perhaps the meaning is best interpreted as 'little lord'. The idd is the same as the udd in Welsh Gruffudd/Maredudd.
However if the name is only pronounced id'n in your family, you probably need to try a book of English surnames or placenames. You should be able to find such a book in your local library, or, if you live near a large university, in the university library. Or you could always try a bookshop :).