Drink provided by commander in short outdoor garment (5)
I believe the answer is:
cocoa
'drink' is the definition.
(I know that cocoa is a drink)
'by commander in short outdoor garment' is the wordplay.
'by' says to put letters next to each other.
'commander' becomes 'co' (commanding officer).
'in short' means to remove the last letter.
'outdoor garment' becomes 'coat'.
'coat' with its last letter taken off is 'coa'.
'co' put next to 'coa' is 'COCOA'.
'provided' is the link.
(Other definitions for cocoa that I've seen before include "product of beans!" , "Powdered cacao seeds" , "brown powder" , "Chocolate powder" , "Evening drink taken in rococo amphitheatre" .)