Spouse briefly taking in a stray (4)
I believe the answer is:
waif
'stray' is the definition.
(I've seen this in another clue)
'spouse briefly taking in a' is the wordplay.
'spouse' becomes 'wife' (wife is a kind of spouse).
'briefly' means to remove the last letter.
'taking in' indicates putting letters inside.
'wife' with its last letter taken away is 'wif'.
'wif' enclosing 'a' is 'WAIF'.
(Other definitions for waif that I've seen before include "Neglected or orphaned child" , "Foundling" , "neglected issue" , "Forsaken child" , "Gamin" .)