Where does “threeside” come from?

threeside (English) comes from English Side, from Middle English side, from Old English sīde, from Proto-West Germanic *sīdā, from Medieval Latin sida, from Late Latin seta, from Latin saeta, from Proto-Italic saitā — to satiate, satisfy.

threeside (English): Any object or shape consisting of three sides;...

Definitions

  1. Any object or shape consisting of three sides;...

Ancestry of “threeside”, step by step

threeside traces back through two separate lines of ancestry.

via English Side

StepLanguageWordMeaning
1EnglishSideA bounding straight edge of a two-dimensional shape
2Middle Englishsidecustom
3Old Englishsīdeside, flank
4Proto-West Germanic*sīdāside
5Medieval Latinsida
6Late LatinsetaAlternative form of saeta; hair, bristle; bristle
7Latinsaetaa bristle, hair on an animal; silk
8Proto-Italicsaitā
9Proto-Indo-Europeanséh₂ito-
10Proto-Indo-Europeansh₂ey-to bind, fetter
11Proto-Indo-Europeanseh₂-to satiate, satisfy

via English three

StepLanguageWordMeaning
1EnglishthreeA numerical value after two and before four....
2Middle Englishthrethree
3Old Englishþrīthree
4Proto-West Germanicþrīʀthree
5Proto-Germanicþrīzthree
6Proto-Indo-European*tréyes
Every word from Proto-Indo-European seh₂-Every word from Proto-Indo-European sh₂ey-Every word from Proto-Indo-European séh₂ito-