Eatery some used in Erith (5)
I believe the answer is:
diner
'eatery' is the definition.
(I've seen this in another clue)
'some used in erith' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'DINER' can be found hidden inside 'used in erith'.
(Other definitions for diner that I've seen before include "(One using) restaurant car" , "One taking a meal" , "one at banquet?" , "US cafe" , "Railway carriage serving meals" .)