"sac in certain fungi," 1830, Modern Latin, from Greek askos "leather bag, wine skin," of unknown origin.
ascus as·cus (ās'kəs)
n. pl. as·ci (ās'ī', -kī')
A membranous, often club-shaped structure in which typically eight spores are formed through sexual reproduction of ascomycetes.
Plural asci (ās'ī', -kī')
A membranous, often club-shaped structure inside which ascospores are formed through sexual reproduction in species of the fungi known as ascomycetes. The ascus is unique to ascomycetes and distinguishes them from other kinds of fungi. Asci are formed when two hyphae that are sexually compatible conjugate. Each ascus typically develops eight ascospores. Asci swell at maturity until they burst, shooting the ascospores into the air.