regimen (n.)

c. 1400, medical, "course of diet, exercise, etc. for sake of health;" mid-15c., "act of governing," from Old French regimen (14c.), from Latin regimen "rule, guidance, government, means of guidance, rudder," from regere "to rule, to direct, keep straight, guide" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule").