Burdened youth sent inside (5)
I believe the answer is:
laden
'burdened' is the definition.
(synonyms)
'youth sent inside' is the wordplay.
'youth' becomes 'lad' (lad means a young man).
'inside' means to look at the middle letters.
The middle of 'sent' is 'en'.
'lad'+'en'='LADEN'
(Other definitions for laden that I've seen before include "Loaded - oppressed" , "Heavily loaded" , "Eland (anag)" , "Like many a cargo ship" , "Filled (with)" .)