Noun

1. A sac-shaped cell present in ascomycete fungi; it is a reproductive cell in which meiosis and an additional cell division produce eight spores.
   • 1967, Constantine. J. Alexopoulos & Harold C. Bold, Algae and Fungi, p.101,

     The one important character which distinguishes the Ascomycetes from all other fungi is the ascus (plural, asci). This is a sac-like structure in which ascospores are formed following karyogamy and meiosis.