Other forms: roiling, roiled
To roil is to churn and stir up violently. The water roiled, roil the sediment, a roiling crowd.
It is used of water, cloud, smoke and crowds, and it suggests turning over from beneath rather than merely moving. Figuratively a market or a party can roil. It is easily confused with roll, which is a different word entirely.
1verbroilTo churn and stir up violently.
“Storm waves roiled the harbour, tossing the small boats against each other.”
roil is a churning.
The origin is uncertain, possibly from an Old French word meaning to make muddy, from a root meaning mud or rust.
Latin
robigo — rust, blight
Vulgar Latin
*robicula
Old French
rouil — mud, rust
Middle French
rouiller — to rust, make muddy
English, today
roil
Origin unknown. Possibly from French - or Middle French rouiller (“to rust, make muddy”), from Old French rouil (“mud, rust”), from Vulgar Latin robicula, from Latin robigo (“rust, blight”)
Etymology from Wiktionary, CC BY-SA
Practised in A Song of Ice and Fire