Token love-bird found in northern lake (7)
I believe the answer is:
nominal
'token' is the definition.
('nominal' can be a synonym of 'token')
'love-bird found in northern lake' is the wordplay.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'bird' becomes 'mina' (mina is a kind of bird**).
'found in' is an insertion indicator.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'lake' becomes 'l'.
'o'+'mina'='omina'
'n'+'l'='nl'
'omina' placed within 'nl' is 'NOMINAL'.
(Other definitions for nominal that I've seen before include "In name only or of token value (7)" , "Ironical understatement (gram mar.)" , "unreal" , "Token - lion man (anag)" , "Titular" .)