<p><strong>noun</strong></p><ul><li>a small sac or cyst.</li><li>Biology: a small bladderlike cavity, especially one filled with fluid.</li><li>Pathology: a circumscribed elevation of the epidermis containing serous fluid; blister.</li><li>Geology: a small, usually spherical cavity in a rock or mineral, formed by expansion of a gas or vapor before the enclosing body solidified.</li></ul>