1A hollow, flexible structure resembling a bag or pouch.

1. 1.1A cavity enclosed by a membrane within a living organism, containing air, liquid, or solid structures.
   ‘In the field of biology, biochemists have been studying vesicles, the small membrane sacs found within cells.’
   More example sentences

   • ‘Fistulas commonly extend from the rectal sac to the perineum or genital tract in a female, or to the urinary tract in a male.’
   • ‘If chemicals are splashed into the eye, the eye and the conjunctival sacs should be washed out immediately with copious amounts of water.’
   • ‘At 8:30 AM, the obstetrician manually broke the patient's amniotic fluid sac in an effort to speed up labor.’
   • ‘Fish make the popping noises by sending air through different chambers of their swim bladders, the inflatable sacs that help fish float.’
   • ‘These protein and lipid molecules are then transported inside lysosomes -- minute, balloon-like sacs within the cell.’
   • ‘The ink sac can make cleaning the squid a bit messy, but all it needs is a good rinse and it's gone.’
   • ‘Sepia comes from the Greek word for the rich reddish-brown pigment obtained from a fluid that is secreted by the cuttlefish from their ink sac.’
   • ‘Worst bit: having to take out the squid's ink sac.’
   • ‘And I think the blisters resemble pomelo pulp sacs.’
   • ‘This is particularly noticeable in the knee and hip where we have big fluid sacs.’
   • ‘Tests have also shown that if a needle is placed into the sac and touches the baby, the baby feels pain and will immediately move away.’
   • ‘The yolk sac was completely absorbed, but the site of attachment was still visible.’
   • ‘‘Surfactant keeps the tiny air sacs in the lungs open,’ Hein says.’
   • ‘For example, the tiny air sacs in lungs expand more than seven times when you inhale.’
   • ‘Scientists also suspect that air pollutants might dampen the growth of alveoli, tiny air sacs in the lungs.’
   • ‘The female was fed one cricket per day until an egg sac was produced.’
   • ‘Each anther cone was gently agitated to release the pollen sacs into the dye solution.’
   • ‘The amniotic sac that contains your baby begins to form about 12 days after conception.’
   • ‘In human beings, the testis is located outside the body in the scrotal sac.’
2. 1.2The distended membrane surrounding a hernia, cyst, or tumor.
   ‘If the leak persists or the aneurysmal sac enlarges, intervention becomes necessary.’
   More example sentences

   • ‘In the vicinity of this mass, there was a hernia sac.’
   • ‘As people get older, fluid-filled sacs, called ‘cysts,’ can form in the kidneys.’
   • ‘PCOS is a hormone problem that can cause the ovaries to become enlarged and develop fluid-filled sacs.’
   • ‘If there is a recurrence (which unfortunately does often happen) then operative removal of the cyst and its sac becomes necessary.’
   • ‘On physical examination, a swollen, fluid-filled sac is noted and palpated over the olecranon.’
   • ‘Alternatively, they can be drained with a needle and syringe, although the sac of the hydrocele may fill with fluid again after a few months.’
   • ‘Essentially, an ovarian cyst is nothing more than a fluid-filled sac, like a blister, on an ovary.’
   • ‘Prior to this Claudius Amyand, physician to Queen Anne, in 1736 successfully removed an acutely inflamed appendix from inside the hernial sac of a young boy.’
   • ‘This procedure meant cutting directly into the back of the knee, tying the damaged artery above and below the aneurysm and scraping out the blood-filled sac.’
   • ‘A visit to the local hospital did not improve matters as the doctor inadvertently punctured a small sac in his elbow which required extensive treatment back in Melbourne.’
   • ‘A cyst is a fluid-filled sac that can grow in any part of the body.’
   • ‘A breast cyst is a fluid-filled sac, like a tiny balloon, inside the breast.’
   • ‘In the distal folds of the hernia sac, a small erosion was noted.’
   • ‘They are swollen, fluid-filled sacs which often become enlarged and painful.’

(in the US) Strategic Air Command.

(in the RAF) Senior Aircraftman or Senior Aircraftwoman.