First recorded in 1735–45; from Latin saccus “bag, sackcloth”; see sack 1
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.
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Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
In a dark room, a doctor pointed to an hourglass shape glowing on the ultrasound screen: There was her amniotic sac, funneling into her dilated cervix, and there was their tiny daughter’s foot, dipping out.
From Salon ● May 27, 2026
Then came the worst part: I passed the amniotic sac.
From The Wall Street Journal ● May 13, 2026
At the inquest on Monday, the court also shown photographs of the area behind a number of houses on the cul de sac.
From BBC ● Jan. 29, 2026
The organism’s various states of evolution — as an egg sac or the Facehuggers that hatch from them — are back too.
From Los Angeles Times ● Aug. 12, 2025
Billy shucked off the sac and found his knife and cut the string.
From "The Red Pony" by John Steinbeck
Now, Sac City sports 70 blooming creations, including entries from the Red Hats women’s group, the sheriff’s office—and the police.
From The Wall Street Journal ● Nov. 26, 2025
"We've got to flush this one down the toilet and get ready for Sac," said Kerr, whose side face the Sacramento Kings in their next match.
From BBC ● Jan. 21, 2025
Boys and girls cross country qualify for CIF Finals next Saturday at My Sac.
From Los Angeles Times ● Nov. 17, 2024
The last bank failure — Citizens Bank, based in Sac City, Iowa — was in November.
From Seattle Times ● Apr. 26, 2024
I see their faces -Greasy Sac and Madge and even the Peacekeepers who buy my meat cheering for us.
From "The Hunger Games" by Suzanne Collins
SAC Relays, where he set a school record and beat the defending state champion, his friend, JJ Harel, of Sherman Oaks Notre Dame.
From Los Angeles Times ● Apr. 27, 2026
SAC Invitational in track and field is set for Saturday at Mt.
From Los Angeles Times ● Apr. 14, 2025
SAC Cross Country Invitational, including in the prominent meet’s team sweepstakes race.
From Los Angeles Times ● Feb. 9, 2025
On a Friday night in September 1971, a group of men, clutching sandwiches and flasks of tea, made their way into SAC, a leather goods shop on Baker Street.
From BBC ● Nov. 16, 2024
At the Air Force’s Strategic Air Command headquarters in Omaha, Nebraska, the SAC commander marched down a concrete ramp into the earth.
From "Fallout: Spies, Superbombs, and the Ultimate Cold War Showdown" by Steve Sheinkin
The Sacs and Fox mined and smelted 60 tons of lead for Shreve.
From Time Magazine Archive
The tribes, or rather fragments of tribes, represented at this meeting, were the Ottawas, Ojibwas, Pottawattamies, Miamis, Sacs, and Wyandots.
From The Conspiracy of Pontiac and the Indian War after the Conquest of Canada by Parkman, Francis
PIT-A-LE-SHAR´-U. In a beautiful wooded region, near the Missouri River, were the villages of the Iowas and Sacs.
From Legends of The Kaw The Folk-Lore of the Indians of the Kansas River Valley by Voe, Carrie de
The Sacs and Foxes are believed to have originally come from the vicinity of Montreal, Canada, about the year 1700, and had lived on or near, Rock Island over one hundred and thirty years.
From Ocean to Ocean on Horseback Being the Story of a Tour in the Saddle from the Atlantic to the Pacific; with Especial Reference to the Early History and Devel by Glazier, Willard W.
Great numbers of the Winnebagoes and of the Sacs and Foxes afterwards arrived, and Gorell addressed them in nearly the same words.
From The Conspiracy of Pontiac and the Indian War after the Conquest of Canada by Parkman, Francis
In another chapter, Mr. Haskell follows the path of an owlet moth into the cranefly orchid’s flower and lets us watch how sacs of pollen attach themselves to the insect’s eye.
From The Wall Street Journal ● Apr. 17, 2026
The spiders’ white egg sacs, usually laid between October and November, are often attached to leaves, tree bark and flat structures and contain 400 to 500 eggs, according to Jorowatch.
From Los Angeles Times ● Apr. 9, 2026
Caitlin and Grace were in different amniotic sacs in the womb, so their parents believed they were fraternal twins.
From BBC ● Feb. 24, 2026
These sacs, known as exosomes, contain RNA that appears to guide tissue repair.
From Science Daily ● Dec. 5, 2025
She drank from the edge of the pool, careful to keep the delicate eggs sacs on her abdomen out of the water.
From "Ceremony:" by Leslie Marmon Silko
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
