Crossword Genius

Hit hard by decaying portal (9)

Ross

I believe the answer is:

threshold

'portal' is the definition.
(thesaurus)

'hit hard by decaying' is the wordplay.
'hit hard' becomes 'thresh'.
'by' says to put letters next to each other.
'decaying' becomes 'old'.
'thresh'+'old'='THRESHOLD'

(Other definitions for threshold that I've seen before include "Doorstep" , "Lower limit" , "Beginning" , "gate" , "Verge" .)

I've seen this clue in The Times.
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