Certainly not descriptive of the hard core! (13)

I believe the answer is:

tenderhearted

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

'certainly not descriptive of the hard' is the definition.
I can't tell whether this definition defines the answer.

'core' is the wordplay.
I cannot really see how this works, but
'core' could be 'heart' (synonyms) and 'heart' is located in the answer.
The remaining letters 'tendered' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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