The story
- Proto-Indo-European*bʰréh₂tēr
- Proto-Germanic*brōþēr
- Proto-West Germanic*brōþer
- Old Englishbrōþor
- Middle Englishbrother
- Englishbrother
- 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ブラザーコンプレックスclip.
- Japaneseブラコン
- English todaybrocon
Borrowed from Japanese ブラコン, clipping of ブラザーコンプレックス, from English brother + complex. By surface analysis, bro + -con (“abnormal sexual attraction”).
Etymology from Wiktionary, CC BY-SA 4.0.