Decline drinks close to one (5)
I believe the answer is:
lapse
'decline' is the definition.
(I've seen this before)
'drinks close to one' is the wordplay.
'drinks' becomes 'laps' (lapping is a kind of drinking).
'close to' indicates one should take the final letters (the close/ending of).
The final letter of 'one' is 'e'.
'laps'+'e'='LAPSE'
(Other definitions for lapse that I've seen before include "unguarded moment" , "moral shortcoming" , "Brief (memory) failure" , "Failing" , "Careless mistake" .)