Origin of condiment, say (6)
I believe the answer is:
'origin' is the definition.
(I know that origin can be written as source)
'condiment say' is the wordplay.
'condiment' becomes 'sauce' (sauce is a kind of condiment).
'say' shows a homophone (sound like).
'sauce' is a homophone of 'SOURCE'.
'of' is the link.
(Other definitions for source that I've seen before include "Origin or starting point" , "Beginning to add" , "Origin; head of stream" , "Origin as of a river" , "From which something springs" .)