Contribution to the regimental salad, say? (6)
I believe the answer is:
radish
'contribution' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'the regimental salad say?' is the wordplay.
'the regimental' becomes 'ra' (I can't justify this - if you can you should believe this answer much more).
'salad say?' becomes 'dish' (salad is a kind of dish).
'ra'+'dish'='RADISH'
'to' is the link.
Can you help me to learn more?
(Other definitions for radish that I've seen before include "Plant with crisp root eaten raw" , "Sir had this vegetable" , "Daikon or mooli" , "Edible small root" , "Pungent, red salad vegetable" .)