(nautical, military, obsolete) A ship of the line or battleship.

(historical) The boundary line between Pennsylvania and Maryland, as run (1764–1767) by Charles Mason and Jeremiah Dixon, that, before abolition, defined part of the northern boundary of states in which slavery was permitted.

(shipbuilding) a model of a vessel formed of boards which are shaped according to the water lines as shown in the plans and laid upon each other to form a solid model

Alternative form of Mason-Dixon Line

Completely; (of belief or acceptance) naively or unquestioningly.

(intransitive, idiomatic) To formalize an agreement.

(curling) The failure to release a stone before crossing the near hog line.

Alternative form of pick-up line

(finance) A line representing the relationship between expected return and systematic risk, thus a graphical representation of the CAPM. It is valid both for portfolios and individual assets.

(idiomatic) Write and send (someone) a note or telegram.