Shift millions before deliveries curtailed (4)
I believe the answer is:
move
'shift' is the definition.
(I know that shift is a kind of move)
'millions before deliveries curtailed' is the wordplay.
'millions' becomes 'm' (abbreviation).
'before' is a charade indicator (letters next to each other).
'deliveries' becomes 'over' (I've seen this before).
'curtailed' means to remove the last letter.
'over' with its final letter removed is 'ove'.
'm'+'ove'='MOVE'
(Other definitions for move that I've seen before include "Change location" , "Relocate" , "Depart" , "Go; change opinion" , "Travel - propose" .)