Give a little drink to a partner without reserve (7)
I believe the answer is:
totally
'without reserve' is the definition.
(I've seen this before)
'give a little drink to a partner' is the wordplay.
'give' means one lot of letters go next to another.
'a little drink' becomes 'tot' (tot can mean a small drink of alcohol).
'to a partner' becomes 'ally' (an ally is an associate or supporter).
'tot'+'ally' is 'TOTALLY'.
(Other definitions for totally that I've seen before include "in every respect" , "Altogether" , "Wholly" , "Absolutely" , "Allowing no exception" .)