Noisy couple on lake capsized (4)
I believe the answer is:
loud
'noisy' is the definition.
('loud' is associated in meaning with 'noisy')
'couple on lake capsized' is the wordplay.
'couple' becomes 'duo' ('duo' can be a synonym of 'couple'**).
'on' means one lot of letters go next to another.
'lake' becomes 'l'.
'capsized' says the letters should be written backwards.
'duo'+'l'='duol'
'duol' written backwards gives 'LOUD'.
(Other definitions for loud that I've seen before include "Tastelessly showy" , "like the bees in Yeats's glade?" , "Resounding" , "Forte" , "booming" .)