(geomorphology) A geomorphologic unconformity marking a boundary between an upland region and a plane; sometimes marked by a series of waterfalls on rivers that cross it.

(physics) any of a series of dark lines in the solar spectrum; due to the absorption of light by atoms and molecules in the Sun's atmosphere

(chiefly Forteana) A supposed alignment of ancient sacred sites, such as megalith structures, along straight lines of mystical power.

Alternative spelling of chatline

(slang, dated) Expressed to someone suffering misfortune.

(slang, dated) Hardship; misfortune.

The edge of the habitat at which trees are capable of growing; the timberline.

(accounting) Total sales or revenue.

(military) A flag on the edge of a minefield. / (linguistics) The line connecting individual letters in Devanagari.

(idiomatic) To set a boundary, rule, or limit, especially on what one will tolerate.