Crossword Genius

It's often abused by grocers dealing with multiples (10)

Ross

I believe the answer is:

apostrophe

'it's often abused by grocers' is the definition.
(reference to the grocers' apostrophe )

I cannot understand how the rest of the clue works.

(Other definitions for apostrophe that I've seen before include "Passage addressed to character" , "Letter omission indicator" , "Mark in exam's" , "It may be superfluous on tradesman's sign" , "At which point discarded letters" .)

I've seen this clue in The Guardian.
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