Give them a plainer tiara if they show such passivity (7)

I believe the answer is:

inertia

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

'passivity' is the definition.
(lack of movement)

'give them a plainer tiara if they show' is the wordplay.
'INERTIA' is hidden in amongst the letters.
However, I'm not sure how the hidden word is indicated.

'such' acts as a link.

Can you help me to learn more?

(Other definitions for inertia that I've seen before include "'Sluggishness, indolence (7)'" , "Passiveness" , "Idling" , "Resistance to motion" , "Listlessness" .)

I've seen this clue in The Irish Times.

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