1. The absence or closure of a normal body orifice or tubular passage such as the anus, intestine, or external ear canal.
2. The degeneration and resorption of one or more ovarian follicles before a state of maturity has been reached.

[New Latin atrēsia : Greek a-, not, without; see a-¹ + Greek trēsis, perforation, orifice.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.