Crossword Genius

Right to take book home once (6)

Ross

I believe the answer is:

libken

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

'home once' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for libken that I've seen is " home in the old days".)

I've seen this clue in The Sunday Times and The Times.
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