English bird on a lake, timeless (7)
I believe the answer is:
eternal
'timeless' is the definition.
('eternal' can be a synonym of 'timeless')
'english bird on a lake' is the wordplay.
'english' becomes 'e' (abbreviation).
'bird' becomes 'tern' (tern is a kind of bird**).
'on' means one lot of letters go next to another.
'lake' becomes 'l'.
'e'+'tern'+'a'+'l'='ETERNAL'
(Other definitions for eternal that I've seen before include "unchanged by time" , "with lasting benefit" , "Never-ending, existing always" , "Timeless" , "like Rome?" .)