Base returning some deliveries (4)
I believe the answer is:
vile
'base' is the definition.
(synonyms)
'returning some deliveries' is the wordplay.
'returning' says the letters should be written in reverse.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'eliv' is hidden within 'deliveries'.
'eliv' in reverse letter order is 'VILE'.
(Other definitions for vile that I've seen before include "Disgusting kind of evil" , "Evil, foul" , "Disgusting, quite evil" , "Live in degenerate way" , "Depraved" .)