Prone to deceive (5)

I believe the answer is:

lying

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'prone' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

(Other definitions for lying that I've seen before include "Anything but upright" , "Prone (to fabrications?)" , "Prone - telling porkies" , "Not being disturbed" , "dishonesty" .)

I've seen this clue in the Evening Standard.

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