Put in grinding toil with hard calculus (10)

I believe the answer is:

enterolith

'calculus' is the definition.
(type of medical calculus, a collection of minerals)

'put in grinding toil with hard' is the wordplay.
'put in' becomes 'enter'.
'grinding' indicates anagramming the letters (letters must be ground into a new form).
'with' says to put letters next to each other.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'toil' is an anagram of 'olit'.
'enter'+'olit'+'h'='ENTEROLITH'

I've seen this clue in The Guardian.

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