M1 hazard causing accident (7)
I believe the answer is:
mistake
'accident' is the definition.
(thesaurus)
'm1 hazard' is the wordplay.
'm1' becomes 'mi' (resembles M1).
'hazard' becomes 'stake' (synonyms).
'mi'+'stake'='MISTAKE'
'causing' acts as a link.
(Other definitions for mistake that I've seen before include "Oversight" , "Slip" , "Error" , "Fault" , "16 down" .)