Where does “undergarb” come from?

undergarb (English) comes from English garb, from Middle French garbe, from Italian garbo, from Frankish garwijan, from Proto-Germanic garwijaną, from Proto-Germanic garwaz, from Proto-Germanic ga-, from Proto-Indo-European ḱóm — resin, gum; to say, speak.

Ancestry of “undergarb”, step by step

undergarb traces back through two separate lines of ancestry.

via English garb

StepLanguageWordMeaning
1EnglishgarbFashion, style of dressing oneself up; A type of...
2Middle Frenchgarbegraceful outline
3Italiangarbopoliteness, gentleness, tact, grace; graceful...
4Frankishgarwijanto make ready; to prepare; to prepare, to ready
5Proto-Germanicgarwijanąto prepare
6Proto-Germanicgarwazready, prepared
7Proto-Germanicga-Indicates association or togetherness; co-;...
8Proto-Indo-Europeanḱómbeside, near, by, with
9Proto-Indo-EuropeanḱeDeictic particle, here; Post-positional...
10Middle Englishkyt
11Germankittputty certain kinds of cement used for fixing e.g. window panes
12Old High Germankuti
13Proto-West Germanickwidugum, resin
14Proto-Germanickweduzresin
15Proto-Indo-Europeangʷet-resin, gum; to say, speak

via English under

StepLanguageWordMeaning
1EnglishunderIn or at a lower level than; As a subject of;...
2Middle Englishunderunder
3Old Englishunderunder, beneath
4Proto-Germanicunderamong, between; under, beneath; under
5Proto-Indo-Europeanh₁entérbetween
6Proto-Indo-Europeanh₁enin; in, inside
Every word from Proto-Indo-European gʷet-
undergarb — Etymology, Origin & Word History | Etymology Explorer