Iroquois tribe (6)
I believe the answer is:
'iroquois tribe' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seneca that I've seen before include "Roman statesman, philosopher and playwright" , "philosopher in Rome" , "Roman stoic; US Indian" , "Stoic, Nero's tutor" , "Dramatist" .)