Boadicea's people (5)
I believe the answer is:
'boadicea's people' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iceni that I've seen before include "Ancient tribesmen" , "Boudica's tribe" , "Old warriors" , "Boadicea's tribe" , "people rebelling against Rome" .)