Where does “underlining” come from?

Underlining comes from English line, from Old English -ing, from Proto-Indo-European līno-, meaning flexible or pliant material.

underlining (English): present participle of underline; An act or...

Definitions

  1. present participle of underline; An act or...

Ancestry of “underlining”, step by step

underlining traces back through two separate lines of ancestry.

via English lining

StepLanguageWordMeaning
1EnglishliningA covering for the inside surface of something;...
2EnglishlineA path through two or more points (compare ‘segment’); a continuous mark, including as made by a pen; any path, curved or straight
3Middle Englishlinerope, cord; line, rule, ruler, measure; rule,...
4Old Englishlīneline, rope, cord; line, cable, rope, hawser,...
5Proto-West Germanic*līnāline, chord, rope, string
6Proto-Germaniclīnǭthat which is made of flax; line, chord, rope,...
7Proto-Germaniclīnąflax
8Proto-Indo-Europeanlīno-flax

via English underline

StepLanguageWordMeaning
1EnglishunderlineA line placed underneath a piece of text in order...
2Englishunder-Beneath, under
3EnglishunderIn or at a lower level than; As a subject of;...
4Middle Englishunderunder
5Old Englishunderunder, beneath
6Proto-Germanicunderamong, between; under, beneath; under
7Proto-Indo-Europeanh₁entérbetween
8Proto-Indo-Europeanh₁enin; in, inside
Every word from Proto-Indo-European līno-