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.

(military) A unit of angular measurement equal to 1/6400 of a complete circle. At 1000 metres one mil subtends about one metre (~0,98 m). Also 1/6000 and 1/6300 are used in other countries.

(mineralogy) A chlorite that contains mostly ferric iron rather than ferrous iron. Leptochlorites are typically richer in trivalent ions relative to silicon and divalent ions.

Alternative form of gravity brightening