Thinner lad working in undeveloped area (10)
I believe the answer is:
hinterland
'undeveloped area' is the definition.
'hinterland' can be an answer for 'area' (hinterland is a kind of area). I am not certain of the 'undeveloped' bit.
'thinner lad working' is the wordplay.
'working' is an anagram indicator.
'thinner'+'lad'='thinnerlad'
'thinnerlad' is an anagram of 'HINTERLAND'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for hinterland that I've seen before include "Remote area of a country" , "Remote inland areas" , "remote country region" , "Remote areas of a country" , "area around a port" .)