The story
- Proto-Indo-European*swé
- Proto-Indo-European*h₁ésh₂r̥
- Proto-Indo-European*su-h₁ésh₂-ōr?
- Proto-Indo-European*swé
- Proto-Indo-European*swésōr
- Proto-Germanic*swestēr
- Proto-West Germanic*swester
- Old Englishsweostor
- Middle Englishsuster
- Englishsister
- Proto-Indo-European*ḱe?
- Proto-Indo-European*ḱóm
- Proto-Italic*kom
- Proto-Italic*kom-
- Latincon-
- Proto-Indo-European*pel-
- Proto-Indo-European*pleḱ-
- Proto-Italic*plektō
- Latinplectō
- Latincomplector
- Latincomplexu
- Frenchcomplexe
- Englishcomplex
- Japaneseシスターコンプレックスclip.
- Japaneseシスコン
- English todaysiscon
Borrowed from Japanese シスコン, clipping of シスターコンプレックス, from English sister + complex. By surface analysis, sis + -con (“abnormal sexual attraction”)
Etymology from Wiktionary, CC BY-SA 4.0.