Deal with a shift Boxing Day (7)
I believe the answer is:
address
'deal' is the definition.
(I know that deal can be written as address)
'a shift boxing day' is the wordplay.
'shift' becomes 'dress' (shift can mean a dress).
'boxing' means one lot of letters goes inside another ('box' can mean contain, as in to put in a box).
'day' becomes 'd' (abbreviation for day).
'dress' going around 'd' is 'ddress'.
'a'+'ddress'='ADDRESS'
'with' acts as a link.
(Other definitions for address that I've seen before include "Discourse" , "Begin to deal with" , "Form of identification for building" , "Art" , "Formal speech" .)