Lag condensed within material (6)

I believe the answer is:

inmate

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

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

'condensed within material' is the wordplay.
'INMATE' is hidden within the letters.
However, I'm uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for inmate that I've seen before include "Convict" , "One in prison/hospital" , "eg Prisoner" , "One is confined to an institution" , "One living in institution" .)

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

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