Mennonite sect (5)
I believe the answer is:
amish
'mennonite sect' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for amish that I've seen before include "Member of a sect" , "US sectarians" , "One 24 [IN-SECT]" , "American religious sect" , "Relating to a strict American sect" .)