Noun
The thin and scarious projection from the upper end of the sheath of a leaf of grass.
A strap-shaped corolla of flowers of Compositae.
A band of white matter in the wall of fourth ventricle of the brain.
Source: Webster's dictionaryA ligule is the strap-shaped tongue of the corolla of either a ray flower or of a ligulate flower. Source: Internet
A membranous appendage or fringe of hairs called the ligule lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath. Source: Internet
Each "petal" consists of a ligule composed of fused petals of an asymmetrical ray flower. Source: Internet
The Cichorioidea has only ray florets, with a 5+0 scheme – all five petals form the ligule. Source: Internet