- A sac.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
Examples from the Web for saccus
Saccus: a lobe of ventral plate of 9th segment in female Lepidoptera.Explanation of Terms Used in Entomology
John. B. Smith