Language used by inhabitant on Guernsey (6)
I believe the answer is:
tongue
'language' is the definition.
(tongue is a kind of language)
'used by inhabitant on guernsey' is the wordplay.
'used by' says the answer is hidden in the clue.
'TONGUE' is hidden in the letters of 'inhabitant on guernsey'.
(Other definitions for tongue that I've seen before include "dialect" , "Muscular tissue in the mouth" , "Organ of taste" , "Mouth organ; language" , "rudely, one could be put out" .)