rule

rule n

OFr riule < L. rēgula, straight stick, bar, ruler, pattern.

1. That which is established as a principle, standard or directory; that by which anything is to be adjusted or regulated, or to which it is to be conformed.
2. In arithmetic and algebra, a determinate mode prescribed for performing any operation and producing a certain result.

rule [-s] v

OFr riuler < L. rēgulāre, to regulate.

1. To govern the movements of things; to conduct; to manage; to control.