Detective Inspectors fail to notice fire (7)
I believe the answer is:
dismiss
'fire' is the definition.
(synonyms)
'detective inspectors fail to notice' is the wordplay.
'detective inspectors' becomes 'DIs' (abbreviation).
'fail to notice' becomes 'miss' (I've seen this in another clue).
'dis'+'miss'='DISMISS'
(Other definitions for dismiss that I've seen before include "Cease to consider" , "Drop" , "Fire - cashier" , "military order" , "Sack (from job)" .)