Diverticulum

n. sac which branches off from a bodily cavity (Anatomy)

A diverticulum (plural: diverticula) is medical term for an outpouching of a hollow (or a fluid filled) structure in the body. It usually implies that the structure is not normally present, i.e. pathological. However, embryologically, some normal structures begin development as a diverticulum arising off of another structure.
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Diverticulum /di·ver·tic·u·lum/ pl. diverti´cula a circumscribed pouch or sac occurring normally or created by herniation of the lining mucous [more]Diverticulum - Community and Resources

Noun
1. a herniation through the muscular wall of a tubular organ (especially the colon)
(hypernym) hernia, herniation
(hyponym) Meckel's diverticulum

n. diverticulum, sac which branches off from a bodily cavity (Anatomy)