Certain to get into drink -- it's deliberate (8)
I believe the answer is:
measured
'deliberate' is the definition.
('measured' can be a synonym of 'deliberate')
'certain to get into drink' is the wordplay.
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'to get into' means one lot of letters goes inside another.
'drink' becomes 'mead' (mead is a kind of drink**).
'sure' going inside 'mead' is 'MEASURED'.
'it's' is the link.
(Other definitions for measured that I've seen before include "Determine dimensions" , "Evaluated" , "Gauged - regulated - steady" , "Having a slow and regular rhythm" , "Sober" .)