... the start of spring, with pest swarming over remains of fire (9)
I believe the answer is:
september
'remains of fire' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'the start of spring with pest swarming' is the wordplay.
'the start of spring' becomes 'ember' (I can't explain this - if you can you should believe this answer much more).
'with' says to put letters next to each other.
'swarming' indicates an anagram.
'pest' anagrammed gives 'sept'.
'ember' put after 'sept' is 'SEPTEMBER'.
'over' is the link.
Can you help me to learn more?
(Other definitions for september that I've seen before include "Last month" , "Tempers be raised this month" , "30 days" , "The longest month?" , "Might tempers be altered this month?" .)