One of relative concern in thermometer manufacture (6)

I believe the answer is:

mother

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

'one of relative' is the definition.
'mother' can be an answer for 'relative' (mother is a kind of relative). I'm unsure of the 'one of' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for mother that I've seen before include "Mum" , "Dam" , "She gave birth to her Tom" , "Be overprotective" , "Nature so-called" .)

I've seen this clue in the Evening Standard.

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