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