'actinomycetous' originates from the Greek word 'aktis' meaning 'ray' and 'mykes' meaning 'fungus', referring to the ray-like structure of the bacteria.

'actinomycetous' changed from the Greek word 'aktinomykēs' and eventually became the modern English word 'actinomycetous'.

Initially, it referred to the ray-like structure of certain fungi, but over time it evolved into its current meaning of relating to actinomycetes.