sac

Everyday

1. A sac is a small bag-like part inside a plant or animal, often filled with liquid or air, like an egg sac or an ink sac. tree →
2. (science) In a spider, an egg sac is a silk bag holding its eggs; in a squid or octopus, the ink sac squirts dark ink to escape enemies. tree →

In the lessons

In science lessons «sac» comes up in life cycles (spider egg sacs, frogspawn), animal defences (the octopus ink sac), the human body (air sacs in the lungs, called alveoli) and plant seeds. It is a science word; in everyday talk people say «bag» or «pouch».

Examples

• The spider guarded its egg sac. tree →
• The octopus squirted ink from its ink sac. tree →
• Our lungs have millions of tiny air sacs. tree →
• Frogs puff up a vocal sac to croak. tree →
• The baby spiders hatched from the egg sac. tree →
• A bee's sting has a venom sac. tree →

Note

Plural «sacs». Homophone trap: «sac» (a bag in a body) and «sack» (a large bag; or to fire someone from a job). Science writing uses «sac».