noun, plural opercula [oh-pur-kyuh-luh] , operculums.
Botany, Zoology. a part or organ serving as a lid or cover, as a covering flap on a seed vessel.
the gill cover of fishes and amphibians. See diag. under fish.
(in many gastropods) a horny plate that closes the opening of the shell when the animal is retracted.

1705–15; < Neo-Latin, Latin: lid, cover, equivalent to oper(īre) to cover + -culum -cule2

opercular, adjective
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World English Dictionary
operculum (əʊˈpɜːkjʊləm)
n , pl -la, -lums
1.  zoology
 a.  the hard bony flap covering the gill slits in fishes
 b.  the bony plate in certain gastropods covering the opening of the shell when the body is withdrawn
2.  botany the covering of the spore-bearing capsule of a moss
3.  biology any other covering or lid in various organisms
[C18: via New Latin from Latin: lid, from operīre to cover]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1713, from L. operculum "cover, lid," from operire "to cover, close" (see weir).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

operculum o·per·cu·lum (ō-pûr'kyə-ləm)
n. pl. o·per·cu·lums or o·per·cu·la (-lə)

  1. Something resembling a lid or cover.

  2. The portions of the frontal, parietal, and temporal lobes covering the insula.

  3. The mucus sealing the endocervical canal of the uterus after conception.

  4. The attached flap in cases of torn retinal detachment.

  5. The mucosal flap partially or completely covering an unerupted tooth.

o·per'cu·lar (-lər) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
operculum   (ō-pûr'kyə-ləm)  Pronunciation Key 
Plural opercula or operculums
A lid or flap covering an opening, such as the gill cover in some fish or the horny flap covering the opening of a snail.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences for operculum
Lampreys and sharks lack an operculum, they have multiple gill openings.
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