Angry characters in stir at Eton (5)
I believe the answer is:
irate
'angry' is the definition.
(similar in meaning)
'characters in stir at eton' is the wordplay.
'characters in' indicates the answer is hidden within the clue.
'IRATE' can be found hidden inside 'stir at eton'.
(Other definitions for irate that I've seen before include "Indignant, angry" , "Angry and incensed" , "Cross, irritated" , "Livid" , "Infuriated" .)