Start or take one drink (6)
I believe the answer is:
origin
'start' is the definition.
(I've seen this in another clue)
'or take one drink' is the wordplay.
'take' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'drink' becomes 'gin' (gin is an alcoholic drink).
'or'+'i'+'gin'='ORIGIN'
(Other definitions for origin that I've seen before include "Point of creation" , "Source, derivation" , "First thing" , "Genesis" , "Source, beginning point" .)