Note small problem in immensity (5)

I believe the answer is:

minim

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'note' is the definition.
(type of musical note)

'small problem in immensity' is the wordplay.
'MINIM' is hidden within the letters.
However, I'm not sure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for minim that I've seen before include "Note of two crotchets" , "Quarter of a breve" , "Palindromic note" , "Double crotchet" , "Musical note - small amount of liquid" .)

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

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