(photography, film, visual arts) A normative rule that an image should be mentally or representationally divided in three horizontally and diagonally, and that the focus of the image should not be in the center of the resulting shape.

(thermodynamics) An empirical rule stating that a linear relationship exists between the temperatures at which two solutions exert the same vapor pressure.

(religion, Wicca) A religious tenet held by some Wiccans, stating that whatever energy, positive or negative, a person puts into the world will be returned threefold.

(mathematics education) A rule stating that, if two ratios are equal, then the denominator of the second equals its numerator times the reciprocal of the first ratio: if a/b=c/d then d=(bc)/a.

The rule of a monarch characterized by a lack of consultation with the parliamentary body of the state.

simple past tense and past participle of rule OK

present participle of rule OK

(evolutionary biology) The principle of biology that states that populations isolated onto islands may undergo evolution towards dwarfism or gigantism to better conform to available resources

(obsolete) Algebra.

(trigonometry) law of cosines