squill, common name for two genera of Old World bulbous plants of the family Liliaceae (lily family). The horticulturists' squill is any plant of the genus Scilla, mostly spring-blooming low herbs with commonly deep blue but also white, rose, or purplish flowers borne along a leafless stem; the leaves are usually narrow. Species of Scilla are naturalized and used in rock gardens and borders; of these, the Siberian squill ( S. sibirica ) has long been a rock-garden favorite. The wood, or wild, hyacinth, called also bluebell or harebell ( S. nonscripta ), is the common squill. The pharmacists' squill, or sea onion ( Urginea maritima ), produces whitish or rose flowers in the autumn before it produces leaves. Its bulbs, collected chiefly from the Mediterranean region, are sold as white or red squill—the white is a drug used as a diuretic, stimulant, and expectorant; the red is used mostly as a rat poison. Squill is classified in the division Magnoliophyta, class Liliopsida, order Liliales, family Liliaceae.