Military assistant has crazy idea to abscond (4-2-4)
I believe the answer is:
aide-de-camp
'military assistant' is the definition.
(I've seen this before)
'crazy idea to abscond' is the wordplay.
'crazy' indicates an anagram.
'to abscond' becomes 'decamp' ('decamp' can be a synonym of 'abscond').
'idea' anagrammed gives 'aide'.
'aide'+'decamp'='AIDE-DE-CAMP'
'has' is the link.
(Other definitions for aide-de-camp that I've seen before include "Military adviser" , "Military assistant" , "Senior officer's assistant" .)