lactationEnglishOxford Dictionary of Englishlactation /lakˈteɪʃn / ▸ noun [mass noun] the secretion of milk by the mammary glands. ▪ the action of suckling an infant. – DERIVATIVES lactational adjective– ORIGIN mid 17th century: from Latin lactatio(n-), from lactare ‘suckle’, from lac, lact- ‘milk’.