(law) A decree issued by the court that becomes absolute at some later date unless cause is shown why it should not.

(physics) the rule which states that the number of degrees of freedom in a system at equilibrium equals the number of components minus the number of phases plus 2

Government by violent gangs, or by the masses.

(idiomatic) A fundamental rule or principle. / (ethics) The principle that one should treat other people in the manner in which one would want to be treated by them.

(chemistry) A rule stating that atoms lose, gain, or share electrons in order to have a full valence shell of 8 electrons. (Hydrogen is excluded because it can hold a maximum of 2 electrons in its valence shell.)

(sports) A rule that ends a one-sided contest prior to its natural conclusion.

A general guideline, rather than a strict rule; an approximate measure or means of reckoning based on experience or common knowledge. / (attributive, usually hyphenated) Approximated, guesstimated.

An unspoken rule.

A rule that is understood to apply but does not exist in written form.

(organic chemistry) A rule describing the outcome of certain addition reactions in organic chemistry.