Single or a large drink (5)
I believe the answer is:
alone
'single' is the definition.
(synonyms)
'a large drink' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'drink' becomes 'one' (eg 'a cold one').
'a'+'l'+'one'='ALONE'
'or' is the link.
(Other definitions for alone that I've seen before include "Without others present" , "On one's own" , "Without friends" , "without partner?" , "Singly" .)