Botany. attached by the base, or without any distinct projecting support, as a leaf issuing directly from the stem.
2.
Zoology. permanently attached; not freely moving.
Origin: 1715–25; < Latinsessilis fit for sitting on, low enough to sit on, dwarfish (said of plants), equivalent to sess(us) (past participle of sedēre to sit1) + -ilis-ile
1725, "adhering close to the surface," from L. sessilis "pertaining to sitting," from sessum, pp. of sedere "to sit" (see sedentary). Meaning "sedentary" first recorded 1860.