Simon with no CID backing involving conjunctions (7)

I believe the answer is:

synodic

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'involving conjunctions' is the definition.
I can't judge whether this defines the answer.

'simon with no cid backing' is the wordplay.
'simon with' becomes 'sy' (I can't explain this - if you can you should give a lot more credence to this answer).
'backing' says the letters should be written in reverse.
'cid' backwards is 'dic'.
'sy'+'no'+'dic'='SYNODIC'

Can you help me to learn more?

(Another definition for synodic that I've seen is " Involving an astronomical conjunction".)

I've seen this clue in The Daily Express.

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