It measures the diameter without any possible aid (5)

I believe the answer is:

meter

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

'it measures' is the definition.
(I've seen this before)

'diameter without any possible aid' is the wordplay.
'METER' is hidden within the letters.
But, I'm unsure how the hidden word is indicated.

'the' acts as a link.

Can you help me to learn more?

(Other definitions for meter that I've seen before include "Measuring device, say for electricity usage" , "Poe sometimes used this" , "Device that measures, say, electricity usage" , "Something measuring" , "Device for recording, say, usage (5)" .)

I've seen this clue in the Evening Standard.

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