Definition of ascus in English:
 ascus
nounPlural asci ˈaskəsˈæskəs
Botany A sac, typically cylindrical in shape, in which the spores of ascomycete fungi develop.
 Example sentencesExamples
-  Fully developed ascospores within intact asci could be identified by their red pigmentation.
 -  Hymenium - the spore-bearing layer of a fruiting body, containing asci, spores and paraphyses.
 -  When mature, a perithecium contains several hundred asci that are ejected by turgor pressure.
 -  Spores were liberated from asci, and vegetative cells were killed, by treatment with glusulase and ethanol.
 -  No mutants had significant numbers of asci with more than four spores.
 
Origin
  
Mid 19th century: modern Latin, from Greek askos 'bag'.