(US, law and law enforcement) a physical or photographic queue of people allegedly involved in a crime, allowing a witness to identify them

(shipbuilding) the outline of a horizontal section of a vessel, as when floating in the water.

(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

(geometry) A line joining centers of figures. / (engineering) A line joining two centers, or fulcra, as of wheels or levers. / A line which determines a dead center.

(engineering) to put in alignment; to put in correct adjustment for smooth running / (transitive) To put things in a line / (intransitive) To get into a line.

(idiomatic) To overstep a boundary, rule, or limit; to go too far or do something unacceptable. / To finish a race. / To achieve completion of something. / To cross the equator, as a vessel at sea.

On a level with the eye of the observer, as of a picture hung in on a wall. / (idiomatic) At risk, as in a contest or enterprise. / Currently calling on the telephone.

Alternative form of Mason-Dixon Line

A spiral marine shell (Fasciolaria distans), of Florida and the West Indies, marked by narrow, dark, revolving lines.