yellow flag
n.
quarantine flag, yellow flag flown by itself by a ship requesting pratique on entering a harbor to indicate that the ship has no disease on board; flag flown by a ship with another flag to indicate that it has contagious or infectious disease aboard; yellow flag raised by a ship that has been quarantined (Shipping); yellow iris (Botany); solid yellow flag used to indicate caution due to dangerous conditions (Car Racing)
Iris pseudacorus
yellow flag
Noun
1. common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated
(synonym) yellow iris, yellow water flag, Iris pseudacorus
(hypernym) iris, flag, fleur-de-lis, sword lily