Grubby relative gets a new start (7)
I believe the answer is:
unclean
'grubby' is the definition.
(similar in meaning)
'relative gets a new start' is the wordplay.
'relative' becomes 'uncle' (uncle is a kind of relative).
'gets' means one lot of letters go next to another.
'start' says to take the initial letters.
The initial letter of 'new' is 'n'.
'uncle'+'a'+'n'='UNCLEAN'
(Other definitions for unclean that I've seen before include "Spotted" , "Defiled" , "Dirty, ritually impure" , "Dirty; immoral" , "taboo" .)