ruling (n.)

c. 1200, "to control, guide, direct, make conform to a pattern," from Old French riuler "impose rule," from Latin regulare "to control by rule, direct," from Latin regula "rule, straight piece of wood," from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule."

The legal sense "establish by decision, lay down authoritatively" is recorded from early 15c. The meaning "mark with parallel straight lines" (with or as with the aid of a ruler) is from 1590s. The slang intransitive sense of "dominate all" is by 1975. "Rule Britannia," patriotic song, is from 1740. Related: Ruled; ruling.