'Regulate' comes from 'regula' (a straight stick) — making rules is straightening. Kin to 'reign' and 'royal.'
To control or direct according to a rule, principle, or system; to adjust the operation of a mechanism to ensure proper functioning.
From Late Latin 'rēgulātus,' past participle of 'rēgulāre' (to direct, to regulate), from Latin 'rēgula' (a rule, a straight stick, a pattern), from 'regere' (to rule, to guide, to keep straight). The PIE root is *h₃reǵ- (to move in a straight line, to direct, to rule), one of the most consequential roots in Western vocabulary, producing 'rex' (king), 'rēgīna' (queen), 'rēgnum' (kingdom), 'rector,' 'reign,' 'royal,' and 'right.' Key roots: regere (Latin: "to rule, to guide, to keep straight"), *h₃reǵ- (Proto-Indo-European: "to move in a straight