Slept again, concealing some small old coins (5)

I believe the answer is:

lepta

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'small old coins' is the definition.
Although both the answer and definition are plural nouns, I cannot see how one could define the other.

'slept again concealing some' is the wordplay.
'some' indicates the answer is hidden within the clue.
'LEPTA' can be found hidden inside 'slept again concealing'.

Can you help me to learn more?

I've seen this clue in The Times.

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