Language used by neighbour dubious (4)
I believe the answer is:
urdu
'language' is the definition.
(Urdu is an example)
'used by neighbour dubious' is the wordplay.
'used by' says the answer is hidden in the clue.
'URDU' can be found hidden inside 'neighbour dubious'.
(Other definitions for urdu that I've seen before include "Analyse and develop (an idea) in detail" , "Form of Hindustani" , "Language akin to Hindi" , "One of official languages of Pakistan" , "Pakistani tongue" .)