The story
- Proto-Indo-European*pleth₂-
- Proto-Indo-European*pléth₂us
- Proto-Hellenic*plətús
- Ancient Greekπλατύς (platús)
- Vulgar Latin*plattus
- Old Frenchplat
- Middle Frenchplat
- Frenchplat
- Frenchfond
- Frenchplafond
- English todayplafond
Borrowed from French plafond (“ceiling”).
Etymology from Wiktionary, CC BY-SA 4.0.