riders is a form of:

Civilian



noun
1.
(A civilian, one not in military or naval services one who is skilled in civil or Roman laws, one who engages in civil suits) ស៊ីវិល (អសេនិក)
adjective
1.
(of a. civilian or civilians) នៃស៊ីវិល
ENGLISH MEANING
noun
1.
One skilled in the civil law.
2.
A student of the civil law at a university or college.
3.
One whose pursuits are those of civil life, not military or clerical.