(geometry) A part of a straight line bounded by two points.

A spectral line resulting from the emission of electromagnetic radiation from an atom or other species as it decays from an excited state to one of lower energy.

plural of main line

Alternative spelling of mainline

plural of rhumb line

(nautical) A line that cuts all meridians at the same angle, the path of a vessel that maintains a constant compass direction.

(fencing) The target area above the opponent's midriff.

Synonym of underscore / (fencing) The target area below the opponent's midriff.

A railway line on which trains travel towards a major terminus.

A railway line on which trains travel away from a major terminus. / (travel, aviation) the next and subsequent flights in an itinerary.