Bladder

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Old English blǣdre, of Germanic origin; related to Dutch blaar and German Blatter, also to blow1.

wiktionary

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From Middle English bladdre, bleddre, bladder, bledder, from Old English blæddre, a variant of blǣdre, blēdre(“blister, bladder”), from Proto-Germanic *blēdrǭ, *bladrǭ(“blister, bladder”); akin to Old High German platara (German Blatter) and Old Norse blaðra (Danish blære), (Norwegian blære).

etymonline

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bladder (n.)

Old English blædre (West Saxon), bledre (Anglian) "(urinary) bladder," also "blister, pimple," from Proto-Germanic *blodram "something inflated" (source also of Old Norse blaðra, Old Saxon bladara, Old High German blattara, German Blatter, Dutch blaar), from PIE root *bhle- "to blow." Extended senses from early 13c. from animal bladders used for buoyancy, storage, etc.