'ascomycetous' originates from Neo-Latin 'Ascomycetes', where the element 'asco-' comes from Greek 'askos' meaning 'sac' and 'myc-' comes from Greek 'mykēs' meaning 'fungus', plus the English suffix '-ous' meaning 'having the quality of'.

'Ascomycetes' was formed in scientific Latin from Greek roots 'askos' + 'mykēs'; the English adjective 'ascomycetous' developed by adding the productive English adjectival suffix '-ous' to the Latinized group name.

Initially it designated 'belonging to or characteristic of the group Ascomycetes'; over time it has remained a technical term used in mycology with the same specialized meaning.