ḱeh₂-s-eh₂
“dwelling, hut, cottage”casino, case, casual
Extended form giving Latin casa, English casino, case, casual, occasion.
Discussion
The PIE form *ḱeh₂-s-eh₂ (dwelling, hut, cottage) is a nominal derivative related to the verbal concept of covering or sheltering, possibly from a root *ḱeh₂- (to cover, to hide). The form gave the word for simple dwelling in several branches — a hut, a cottage, a basic shelter.
The most productive descendant is the Latin derivative casa (hut, cottage — a simple rural dwelling), which survived into all the Romance languages: Italian casa (house — elevated from "hut" to the standard word for house, displacing Latin domus), Spanish casa (house), Portuguese casa, and French chez (at the home of — from Latin *ad casa, literally "to the cottage"). The French chez is one of the most commonly used prepositions in the language, and it descends from the PIE word for a humble hut — a striking example of semantic elevation.
English borrowed from the same family through multiple channels: casino (Italian, originally a small house or summer house, then a social club, then a gambling establishment — the semantic journey from cottage to casino in four steps), and the archaic English casement (a window frame, possibly from casa-ment, a house-fitting, though some derive it from encase).
German Haus (house) and English house (OE hūs) are sometimes connected to this root through PGmc *hūsą, though the phonological derivation from *ḱeh₂-s- requires assumptions about the laryngeal treatment that not all scholars accept. If the connection holds, then house and casa are cognates — the Germanic and Romance words for dwelling sharing a common PIE ancestor. If it does not hold, then PGmc *hūsą is of uncertain etymology, and the resemblance to *ḱeh₂-s- is coincidental.
The word's semantic range from hut to house to casino traces the architectural history of European civilisation: what began as a basic shelter became the standard dwelling, then a social venue, then a place of entertainment. The PIE speakers who named their simple shelters could not have foreseen that their word would eventually denote the glittering halls of Monte Carlo.