dialectology
Concise Oxford English Dictionary © 2008 Oxford University Press:
dialectology /ˌdʌɪəlɛkˈtɒlədʒi/
▶noun the branch of linguistics concerned with the study of dialects.
– derivatives
dialectological /-təˈlɒdʒɪk(ə)l/ adjective,
dialectologist noun.
dialectological /-təˈlɒdʒɪk(ə)l/ adjective,
dialectologist noun.
'dialectology' also found in these Oxford entries:

