Engineer tied circle that provides insulation (10)

I believe the answer is:

dielectric

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'engineer tied circle that provides insulation' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'engineer tied circle' is the wordplay.
'engineer' indicates anagramming the letters.
'tied'+'circle'='tiedcircle'
'tiedcircle' with letters rearranged gives 'DIELECTRIC'.

Can you help me to learn more?

(Another definition for dielectric that I've seen is " Insulator, derelict IC (anag.)".)

I've seen this clue in The Irish Times.

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