Item maybe misplaced by greengrocer or a pet shop, strangely (10)
I believe the answer is:
apostrophe
'item maybe misplaced by greengrocer' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'or a pet shop strangely' is the wordplay.
'strangely' indicates anagramming the letters.
'or'+'a'+'pet'+'shop'='orapetshop'
'orapetshop' anagrammed gives 'APOSTROPHE'.
Can you help me to learn more?
(Other definitions for apostrophe that I've seen before include "Passage addressed to character" , "Mark showing omission of letters" , "Single quote mark" , "Where character may be absent" , "Mark in exam's" .)