Keep cool about great fire spreading (11)
I believe the answer is:
refrigerate
'keep cool' is the definition.
('refrigerate' can be a synonym of 'keep cool')
'about great fire spreading' is the wordplay.
'about' becomes 're' (regarding**).
'spreading' indicates anagramming the letters.
'great'+'fire'='greatfire'
'greatfire' anagrammed gives 'frigerate'.
're'+'frigerate'='REFRIGERATE'
(Other definitions for refrigerate that I've seen before include "Keep (food or drink) cold" , "Freeze" , "Provide cooling" , "Chill" , "Cool!" .)