Crossword Genius

Nourishing sausage ingredient if nothing more (4)

Ross

I believe the answer is:

sago

I'm a little stuck... Click here to teach me more about this clue!

'nourishing sausage ingredient' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'if nothing more' is the wordplay.
'if' becomes 'sag' (I can't explain this - if you can you should give a lot more credence to this answer).
'nothing more' becomes 'O' (resembles 0).
'sag'+'o'='SAGO'

Can you help me to learn more?

(Other definitions for sago that I've seen before include "Palm cereal" , "Starchy cereal used in puddings" , "Edible palm starch" , "Starchy grain used in desserts" , "Powdery starch from a palm" .)

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