[1] : The Collaborative International Dictionary of English v.0.48

sessile \ses"sile\, a. l. sessilis low, dwarf, from sedere,
   sessum, to sit: cf. f. sessile.
   1. attached without any sensible projecting support.
      1913 webster

   2. bot. resting directly upon the main stem or branch,
      without a petiole or footstalk; as, a sessile leaf or
      blossom.
      1913 webster

   3. zool. permanently attached; -- said of the gonophores of
      certain hydroids which never became detached.
      1913 webster

[2] : WordNet (r) 2.0

sessile
     adj 1: permanently attached to a substrate; not free to move about;
            "an attached oyster"; "sessile marine animals and
            plants" syn: attached ant: vagile
     2: attached directly by the base; not having an intervening
        stalk; "sessile flowers"; "the shell of a sessile barnacle
        is attached directly to a substrate" syn: stalkless
        ant: pedunculate
see also:
attached vagile stalkless pedunculate 

Sessile >> S Words
Sessile, definition of term: Sessile
sessile_pag1.html