n. A thin, elastic, highly distensible and contractile muscular and membranous sac forming that portion of the urinary passages in which urine, constantly secreted by the kidneys, is retained until it is discharged from the body.n. Any similar receptacle, sac, or vesicle, commonly distinguished by a qualifying prefix. See air-bladder, brain-bladder, gall-bladder, swim-bladder.n. Any vesicle, blister, bleb, blain, or pustule containing fluid or air.n. In botany: A hollow membranous appendage on the leaves of Utricularia, filled with air and floating the plant.n. A cellular expansion of the substance of many algæ filled with air. See cut under air-cell.n. Anything inflated, empty, or unsound: as, “bladders of philosophy,”To put up in a bladder: as, bladdered lard.To puff up; fill, as with wind.n. A membranous inflated fruit, as that of Kœlreuteria or the pericarp of Physalis.