Cracker show held in last third of August (6)
I believe the answer is:
sexpot
'last third of august' is the definition.
The definition suggests a singular noun which matches the answer.
'cracker show held' is the wordplay.
'cracker' becomes 'st' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'show' becomes 'expo' (short for exposition, a large exhibition).
'held' indicates putting letters inside.
'st' going around 'expo' is 'SEXPOT'.
'in' is the link.
Can you help me to learn more?
(Other definitions for sexpot that I've seen before include "Babe" , "Dishy type" , "Hot bit of stuff" , "Desirable" , "eg Craig? Lopez?" .)