One's capacity for it? (6)

I believe the answer is:

libido

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'capacity for it?' is the definition.
(capacity for sex, euphemistically called 'it')

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(Other definitions for libido that I've seen before include "Emotional energy associated with sexual desire" , "Natural urges" , "Sexual drive" , "Sexual impulse" , "Psychic, sexual, energy" .)

I've seen this clue in The Telegraph.

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