Single allowance given to married traveller (7)
I believe the answer is:
migrant
'traveller' is the definition.
(migrant is a kind of traveller)
'single allowance given to married' is the wordplay.
'single' becomes 'i' (one).
'allowance' becomes 'grant' (I've seen this before).
'given to' means one lot of letters go next to another.
'married' becomes 'm'.
'i'+'grant'='igrant'
'igrant' after 'm' is 'MIGRANT'.
(Other definitions for migrant that I've seen before include "Changing habitat (bird)" , "Person who has moved residence to another place" , "Ring mat (anag.)" , "relocating" , "Animal moving with the seasons" .)