perimysiumPronunciation: /ˌpɛrɪˈmɪsɪəm/Definition of perimysium noun [mass noun] Anatomy the sheath of connective tissue surrounding a bundle of muscle fibres. Derivatives perimysial adjective Origin: mid 19th century: modern Latin, from Greek peri- 'around' + mus 'muscle'perimysium in other Oxford dictionaries Definition of perimysium in the US English dictionary