Concoct a lie partly related to eight (5)

I believe the answer is:

octal

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'related to eight' is the definition.
I can't judge whether this definition defines the answer.

'concoct a lie partly' is the wordplay.
'partly' says the answer is hidden in the clue (part of the clue is used).
'OCTAL' is hidden within 'concoct a lie'.

Can you help me to learn more?

(Other definitions for octal that I've seen before include "based on eights" , "with unusual base" , "(Of maths) in base eight" , "Using 8 as base (maths)" , "Working in base 8" .)

I've seen this clue in the Sydney Morning Herald.

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