from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A case, covering, or sheath, such as the covering of the pollen sacs of an anther or the thick cell wall of certain dinoflagellates.

from The Century Dictionary.

  • noun A case; box; sheath.
  • noun [capitalized] A genus of pteropods, having a sheath-like shell, typical of the family Thecidæ. Sowerby, 1845. Also named Hyolithes (Eichwald, 1840).
  • noun In the graptolites, one of the receptacles of the zoöids.

from the GNU version of the Collaborative International Dictionary of English.

  • noun A sheath; a case
  • noun The chitinous cup which protects the hydranths of certain hydroids.
  • noun The more or less cuplike calicle of a coral.
  • noun The wall forming a calicle of a coral.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun biology Any external case or sheath.
  • noun botany The pollen producing organ usually found in pairs and forming an anther.
  • noun medicine The twin layers of cells surrounding the basal lamina of an ovarian follicle
  • noun microbiology, planktology The membrane complex enveloping the cells of certain plankton including diatoms and dinoflagellates
  • noun marine biology The calcareous wall of a corallite, the exoskeleton of a coral polyp

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

  • noun outer sheath of the pupa of certain insects
  • noun a case or sheath especially a pollen sac or moss capsule


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

[Latin thēca, case, receptacle, from Greek thēkē; see dhē- in Indo-European roots.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From New Latin, from Latin theca, from Ancient Greek θήκη (thēkē, "a case, box, receptacle"), from τίθημι (tithēmi, "put, set, place").


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  • Fully formed ovarian follicle: • Outside the theca interna some fibrous tissue becomes condensed to form another covering for the follicle called the theca externa.

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  • Last year we found and bought a second hand relic, some fabric from the blanket which St Therese used set in a silver theca itself set in a monstrance style stand.

    Visit of St Thérèse relics 2009

  • Bibliographies of alchemical texts date from an early period, but the two standard lists are J. Ferguson, Biblio - theca Chemica, 2 vols.


  • The medulla oblongata not growing so hard as the spinalis, was doubtless owing to its not being confined in an osseous theca, but surrounded with soft parts, which allowed it room to spread.

    An Essay on the Shaking Palsy James Parkinson

  • But of what nature that morbid change is; and whether originating in the medulla itself, in its membranes, or in the containing theca, is, at present, the subject of doubt and conjecture.

    An Essay on the Shaking Palsy James Parkinson

  • Hence therefore may proceed inflammation of quicker or of slower progress, disease of the vertebræ, derangement of structure in the medulla, or in its membranes, thickening or even ulceration of the theca, effusion of fluids, &c.

    An Essay on the Shaking Palsy James Parkinson

  • The result of this would be a thickening of the theca, or membranes, and perhaps an increase in the volume of the medulla itself, which would gradually occasion such a degree of pressure against the sides of the unyielding canal, as must eventually intercept the influence of the brain upon the inferior portion of the medullary column, and upon the parts on which the nerves of this portion are disposed.

    An Essay on the Shaking Palsy James Parkinson

  • The various forms therefore may not depend proximately on fructification itself, but on the peculiar growth given to the species, in the same way in fact as we have the numerous modifications of the theca in mosses, etc. and the infinite modifications of the carpels in Phaenogams.

    Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries William Griffith

  • But taking all circumstances into due consideration, particularly the very gradual manner in which the disease commences, and proceeds in its attacks; as well as the inability to ascribe its origin to any more obvious cause, we are led to seek for it in some slow morbid change in the structure of the medulla, or its investing membranes, or theca, occasioned by simple inflammation, or rheumatic or scrophulous affection.

    An Essay on the Shaking Palsy James Parkinson

  • Assuming however the state just mentioned as the proximate cause, it may be concluded that this may be the result of injuries of the medulla itself, or of the theca helping to form the canal in which it is inclosed.

    An Essay on the Shaking Palsy James Parkinson


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