Note in second book, we had on description of exoskeleton (9)

I believe the answer is:

chitinous

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'on description of exoskeleton' is the definition.
I can't tell whether this definition defines the answer.

'note in second book we' is the wordplay.
'note' becomes 'chit' (I've seen this before).
'second book' becomes 'o' (2nd letter of 'book').
'we' becomes 'us'.
'chit'+'in'+'o'+'us'='CHITINOUS'

'had' acts as a link.

Can you help me to learn more?

I've seen this clue in The Hindu.

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