Removing hair that is growing fast (6)

I believe the answer is:

waxing

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'growing fast' is the definition.
'waxing' can be an answer for 'growing' (thesaurus). I am not sure about the 'fast' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Another definition for waxing that I've seen is " (Of moon) increasing".)

I've seen this clue in The Hindu.

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