Furtive about cooker left dirty (8)
I believe the answer is:
slovenly
'dirty' is the definition.
(thesaurus)
'furtive about cooker left' is the wordplay.
'furtive' becomes 'sly' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'cooker' becomes 'oven' (synonyms).
'left' becomes 'l' (common abbreviation).
'oven'+'l'='ovenl'
'sly' placed around 'ovenl' is 'SLOVENLY'.
(Other definitions for slovenly that I've seen before include "Dirty and slipshod" , "Untidy, careless" , "Untidy, unkempt" , "Disorganised" , "Like a slob" .)