Eatery some used in error (5)
I believe the answer is:
diner
'eatery' is the definition.
(thesaurus)
'some used in error' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'DINER' is hidden in the letters of 'used in error'.
(Other definitions for diner that I've seen before include "US eatery" , "Eater" , "Restaurant customer" , "Restaurant client" , "One taking a meal" .)