Marvellous old queen in pursuit of drink (5)
I believe the answer is:
super
'marvellous' is the definition.
(I've seen this before)
'old queen in pursuit of drink' is the wordplay.
'old queen' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'in pursuit of' means one lot of letters go next to another (some letters chase after others).
'drink' becomes 'sup' (to sup is to drink).
'er' put after 'sup' is 'SUPER'.
(Other definitions for super that I've seen before include "Top" , "Peachy" , "Excellent - small-part actor" , "Informally great, really up there" , "Peerless" .)