Neglect to order the thing in question (4)
I believe the answer is:
omit
'neglect' is the definition.
(I know that neglect can be written as omit)
'order the thing in question' is the wordplay.
'order' becomes 'om' (Order of Merit).
'the thing in question' becomes 'it' (I am not sure about this - if you are sure you should believe this answer much more).
'om'+'it'='OMIT'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for omit that I've seen before include "Leave out, perhaps in error" , "Disregard" , "Fail to include" , "Leave out or overlook" , "by-pass" .)