From Latin 'linea' (linen thread), from 'linum' (flax) — geometry that began as a piece of string pulled taut.
A long narrow mark or band; a length of cord, rope, or wire; a row of people or things; a connected series of military fieldworks; an ancestry or lineage.
English 'line' has a double ancestry. Old English 'līne' (a rope, a series, a rule) was borrowed from Latin 'līnea' (a linen thread, a string, a line drawn with a string), which derived from 'līnum' (flax, linen). The ultimate root is Proto-Indo-European *līno- (flax). The semantic path runs from the flax plant to the thread spun from it to the straight mark that a taut thread creates. A geometric line is, at its etymological heart, a piece of string
A geometric 'line' is etymologically a piece of string: Latin 'līnea' meant 'a thread made of flax.' Ancient builders and surveyors created straight lines by stretching linen cords between two points — the word preserves this practical technique. 'Linen,' 'linseed,' and 'lingerie' are all relatives.