Primordial matter found in mouldy lemons (4)
I believe the answer is:
ylem
'primordial matter' is the definition.
(I've seen this in another clue)
'in mouldy lemons' is the wordplay.
'in' indicates a hidden word.
'YLEM' is hidden within 'mouldy lemons'.
'found' is the link.
(Other definitions for ylem that I've seen before include "Big Bang material" , "Substance" , "proto-matter, supposedly" , "Original matter" .)