Where does “undercap” come from?

undercap (English) comes from English Cap, from English Capricorn, from French Capricorne, from Latin Capricornus, from Latin caper, from Proto-Italic *kapros, from Proto-Indo-European kápros — he-goat, billy goat.

Ancestry of “undercap”, step by step

undercap traces back through two separate lines of ancestry.

via English Cap

StepLanguageWordMeaning
1EnglishCapA nickname for the captain of a team, ship, etc
2EnglishCapricornSomeone with a Capricorn star sign
3FrenchCapricorneCapricorn
4LatinCapricornusCapricornus, the constellation of the zodiac
5Latincapera male goat, billy goat; vocative singular of...
6Proto-Italic*kaproshe-goat
7Proto-Indo-Europeankáproshe-goat, billy goat

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 káprosEvery word from Proto-Italic *kaprosEvery word from Latin caper