And some primordial soup (4)
I believe the answer is:
also
'and' is the definition.
'some primordial soup' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ALSO' can be found hidden inside 'primordial soup'.
(Other definitions for also that I've seen before include "'Besides, moreover (4)'" , "Likewise" , "Item" , "an indication of more to come" , "in accompaniment" .)