Plural of bladder; flexible sac-like organs in animals that store urine or gas, or any pouch-like container.
From Old English 'blædre,' related to Germanic roots meaning 'to blow' or 'swell.' The word evolved to describe any inflatable or expandable sac in biology, from Middle English through to modern usage.
Fish have swim bladders filled with gas that let them float at different depths—it's like an internal elevator! Medieval people even used actual animal bladders as balloons and water containers before rubber was invented.
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