Litre in tankard to pick up and down (4)
I believe the answer is:
glum
'down' is the definition.
(thesaurus)
'litre in tankard to pick up' is the wordplay.
'litre' becomes 'l' ('l' can be a synonym of 'litre').
'in' means one lot of letters goes inside another.
'tankard' becomes 'mug' (I've seen this before).
'to pick up' says the letters should be written backwards.
'l' going inside 'mug' is 'mulg'.
'mulg' back-to-front is 'GLUM'.
'and' is the link.
(Other definitions for glum that I've seen before include "Unhappy" , "Forlorn" , "In low spirits" , "Doleful" , "Sad, down-in-th-mouth" .)