Old Spanish man drinks one (6)
I believe the answer is:
senior
'old' is the definition.
(I know that old can be written as senior)
'spanish man drinks one' is the wordplay.
'spanish man' becomes 'senor' (I've seen this in another clue).
'drinks' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'senor' going around 'i' is 'SENIOR'.
(Other definitions for senior that I've seen before include "Higher in status" , "Elder (of two)" , "Superior - elder" , "Older or higher in standing" , "Being old" .)