The rule that the best video games are easy to learn but difficult to master.

(phonology) A sound change and a synchronic phonological rule that operated during an early stage of the Proto-Indo-European language. The rule deleted coda fricatives *s or laryngeals *h₁, *h₂ or *h₃ (cover symbol *H), with compensatory lengthening occurring in a word-final position.

Alternative form of Charles's law

(economics) A principle whereby those who produce anything must be paid sufficiently to buy the products they make, whether it be in a local economy or the world economy.

plural of lawful day

(historical) Any day on which business could be legally done, excluding Sundays and public holidays.

plural of aunt-in-law

(nonstandard) The wife of one's uncle or aunt (parent's sibling). / The aunt of one's husband. / The aunt of one's wife.

The observation that a person can expect to experience an event with odds of one in a million approximately once per month.

(archaic) Brothers-in-law