Sartre novel about ordinary hot day (7)
I believe the answer is:
roaster
'hot day' is the definition.
(thesaurus)
'sartre novel about ordinary' is the wordplay.
'novel' indicates anagramming the letters.
'about' indicates putting letters inside.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'sartre' with letters rearranged gives 'raster'.
'raster' placed around 'o' is 'ROASTER'.
(Other definitions for roaster that I've seen before include "cooker" , "Oven-ready bird" , "oven item" , "A resort (anag.)" , "Fowl for the oven" .)