heteronym

Concise Oxford English Dictionary © 2008 Oxford University Press:
heteronym /ˈhɛtərə(ʊ)nɪm/

▶noun Linguistics

• 1 each of two or more words which are spelled identically but have different sounds and meanings (e.g. tear1 and tear2).

• 2 each of two or more words which are used to refer to the identical thing in different geographical areas of a speech community, e.g. nappy and diaper.

– derivatives
heteronymic adjective,
heteronymous adjective.