Neglect to put it on order (4)
I believe the answer is:
omit
'neglect' is the definition.
(I know that neglect can be written as omit)
'it on order' is the wordplay.
'on' means one lot of letters go next to another.
'order' becomes 'om' (Order of Merit).
'it' after 'om' is 'OMIT'.
'to put' acts as a link.
(Other definitions for omit that I've seen before include "Exclude; forget to include" , "Leave out or forget" , "Leave out or overlook" , "Miss out" , "Leave out, perhaps in error" .)