Coagulant affected their neck (9)

I believe the answer is:

thickener

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'coagulant' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?

'affected their neck' is the wordplay.
'affected' is an anagram indicator.
'their'+'neck'='theirneck'
'theirneck' anagrammed gives 'THICKENER'.

Can you help me to learn more?

(Other definitions for thickener that I've seen before include "Cornflour, for example" , "Such as cornflour in cooking" , "cornflour, perhaps" .)

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

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