Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • adj. Botany Stalkless and attached directly at the base: sessile leaves.
  • adj. Zoology Permanently attached or fixed; not free-moving: a sessile barnacle.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. permanently attached to a substrate; not free to move about; “an attached oyster”
  • adj. attached directly by the base; not having an intervening stalk.

from the GNU version of the Collaborative International Dictionary of English

  • adj. Attached without any sensible projecting support.
  • adj. Resting directly upon the main stem or branch, without a petiole or footstalk.
  • adj. Permanently attached; -- said of the gonophores of certain hydroids which never became detached.

from The Century Dictionary and Cyclopedia

  • In botany, attached without any sensible projecting support; sitting directly on the body to which it belongs without a support; attached by the base: as, a sessile leaf, one issuing directly from the main stem or branch without a petiole or footstalk; a sessile flower, one having no peduncle; a sessile stigma, one without a style, as in the poppy.
  • In zoöl. and anatomy:
  • Seated flat or low; fixed by a broad base; not stalked or pedunculated.
  • Fixed; not free; sedentary.
  • Specifically, in Crustacea: Having no peduncle, as a cirriped; belonging to the Sessilia. Having no stalk or ophthalmite, as an eye.
  • In conchology, having no stalk or ommatophore, as an eye.
  • In entomology, not petiolate, as an abdomen.
  • In Hydroida, not detachable or separable, as a gonophore.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adj. attached directly by the base; not having an intervening stalk
  • adj. permanently attached to a substrate; not free to move about

Etymologies

Latin sessilis, low, of sitting, from sessus, past participle of sedēre, to sit.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From New Latin sessīlis ("sitting"), from sessus, perfect passive participle of verb sedēre ("sit"), + adjective suffix -īlis. Compare session. (Wiktionary)

Examples

  • The ganglia had already finished migrating to three new positions, repeating the same spherical configuration each time, before Richard recognized that what was growing in the sessile was a manna melon.

    The Garden of Rama

  • Perhaps, Richard mused, the sessile is a recording device only, and is incapable of imagination.

    The Garden of Rama

  • They may be sessile, that is, the cup rests immediately on the ground or wood, or leaves, or they may possess a short, or rather long stalk.

    Studies of American Fungi. Mushrooms, Edible, Poisonous, etc.

  • From these lateral stemmed species there is an easy transition to the stemless forms which are sessile, that is, the shelving forms where the pileus is itself attached to the trunk, or other object of support on which it grows.

    Studies of American Fungi. Mushrooms, Edible, Poisonous, etc.

  • The term _sessilifolius_ has been given to this species of Cytisus, because the leaves are for the most part sessile, that is sit close to the branches, without any or very short footstalks; such they are at least on the flowering branches when the shrub is in blossom, but at the close of the summer they are no longer so, the leaves acquiring very evident footstalks.

    The Botanical Magazine Vol. 8 Or, Flower-Garden Displayed

  • Serrated colorectal polyps include the subgroups hyperplastic polyps, sessile serrated polyps (also called sessile serrated adenomas), and serrated adenomas.

    EurekAlert! - Breaking News

  • That alien face - it supposely has a "sessile" compound eye, by which it is meant - not on a stalk.

    April 2010

  • Many ponds are seasonal, lasting just a couple of months (such as sessile pools) while lakes may exist for hundreds of years or more.

    Freshwater biomes

  • Clover is a pair of leaves; the blossom is said to be "sessile" or seated on these leaves.

    Wildflowers of the Farm

  • Do legislators imagine that pedophiles are sessile creatures, like sea anemones or Venus fly-traps, and have to wait passively for their victims to come withreach?

    The Volokh Conspiracy » Where, According to Tort Law, Should Accused Criminals and Ex-Convicts Live?

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  • "Sessile oak, beech and silver birch crowd around the sandy track, the sunlight twinkles from between the interlocking boughs, the little boys cavort, the adolescents even begin to frolic a bit."
    Psychogeography by Will Self, 154

    Note that the Sessile Oak is a thing unto itself, but in the course of looking it up I looked up the general meaning of "sessile" too.

    October 17, 2010

  • Oxford University Press

    adj. (Biology) permanently attached to a substrate; not free to move about: “an attached oyster”: sesile marine animals and plants”

    monocytes, like all blood cells, are born in the bone marrow and at some point migrate to the spleen, lured by cues yet to be identified. They sit and wait, a sessile bunch, but when aroused by such chemical signatures of damage as angiotensin, the cells surge forth without hesitation

    August 4, 2009