Despicable blokes initially tenanted bottom floor? (8)
I believe the answer is:
basement
'bottom floor?' is the definition.
(I've seen this before)
'despicable blokes initially tenanted' is the wordplay.
'despicable' becomes 'base' (synonyms).
'blokes' becomes 'men' (bloke can informally mean a man).
'initially' suggests taking the first letters.
The initial letter of 'tenanted' is 't'.
'base'+'men'+'t'='BASEMENT'
(Other definitions for basement that I've seen before include "Floor below ground level" , "Man beset in bottom of house" , "Japanese medicine box" , "space below stairs" , "Lowest floor of a building" .)