sac

/sæk/

/sæk/

Other forms: sacs

A sac is a hollow space or container. While any pocket or pouch can be called a sac, the word usually refers to a small enclosed space that occurs in nature, like a spider's egg sac or a squid's ink sac.

You might put your groceries in a sack, but without the “k” a sac is smaller and attached to a plant or animal. Human fetuses grow inside an amniotic sac, and seed plants produce pollen inside sacs as well. Since the mid-1700s, sac has been used to mean "biological pocket," from the Latin root word saccus, or "bag." If you’re not sure which sac to use, it’s almost always the other one unless you’re in biology class.

Definitions of sac

1. noun

   an enclosed space
   synonyms: pocket, pouch, sack

   type of:

   cavity, enclosed space

   space that is surrounded by something
2. noun

   a case or sheath especially a pollen sac or moss capsule
   synonyms: theca

   type of:

   cover, covering, natural covering

   a natural object that covers or envelops
3. noun

   a structure resembling a bag in an animal
   types:

   yolk sac

   membranous structure enclosing the yolk of eggs in birds, reptiles, marsupials, and some fishes; circulates nutrients to the developing embryo

   umbilical vesicle, vesicula umbilicus, vitelline sac, yolk sac

   membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional

   amnion, amnios, amniotic sac

   thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)

   chorion

   the outermost membranous sac enclosing the embryo in higher vertebrates (reptiles, birds and mammals)

   coelenteron

   the saclike body cavity of a coelenterate

   air bladder, float, swim bladder

   an air-filled sac near the spinal column in many fishes that helps maintain buoyancy

   air sac

   any of the membranous air-filled extensions of the lungs of birds

   air sac

   any of the thin-walled extensions of the tracheae of insects

   saccule, sacculus

   a small sac or pouch (especially the smaller chamber of the membranous labyrinth)

   bladder, vesica

   a distensible membranous sac (usually containing liquid or gas)

   acinus

   one of the small sacs or saclike dilations in a compound gland

   bursa

   a small fluid-filled sac located between movable parts of the body especially at joints

   cistern, cisterna

   a sac or cavity containing fluid especially lymph or cerebrospinal fluid

   pocket, pouch

   (anatomy) saclike structure in any of various animals (as a marsupial or gopher or pelican)

   cyst, vesicle

   a small anatomically normal sac or bladderlike structure (especially one containing fluid)

   air cell, air sac, alveolus

   a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways

   pericardial sac

   the membrane surrounding the heart

   gastric mill, gizzard, ventriculus

   thick-walled muscular pouch below the crop in many birds and reptiles for grinding food

   utricle, utriculus

   a small pouch into which the semicircular canals open

   dacryocyst, lacrimal sac, tear sac

   either of the two dilated ends of the lacrimal ducts at the nasal ends of the eyes that fill with tears secreted by the lacrimal glands

   gall bladder, gallbladder

   a muscular sac attached to the liver that stores bile (secreted by the liver) until it is needed for digestion

   atrial auricle, auricle, auricula atrii

   a small conical pouch projecting from the upper anterior part of each atrium of the heart

   auricula, auricular appendage, auricular appendix

   a pouch projecting from the top front of each atrium of the heart

   Golgi apparatus, Golgi body, Golgi complex, dictyosome

   a netlike structure in the cytoplasm of animal cells (especially in those cells that produce secretions)

   urinary bladder

   a membranous sac for temporary retention of urine

   cheek pouch

   a membranous pouch inside the mouth of many rodents (as a gopher)

   marsupium

   an external abdominal pouch in most marsupials where newborn offspring are suckled

   scrotum

   the external pouch that contains the testes

   bleb, blister, bulla

   (pathology) an elevation of the skin filled with serous fluid

   follicle

   any small spherical group of cells containing a cavity

   liposome

   an artificially made microscopic vesicle into which nucleic acids can be packaged; used in molecular biology as a transducing vector

   type of:

   bodily cavity, cavity, cavum

   (anatomy) a natural hollow or sinus within the body