ichneumonEnglishOxford New American Dictionaryichneumon /ikˈn(y)o͞omən, ɪkˈn(j)umən / ▸ noun 1 (also ichneumon wasp or ichneumon fly) a slender parasitic wasp with long antennae, which deposits its eggs in, on, or near the larvae of other insects. Family Ichneumonidae, order Hymenoptera: numerous genera and species. 2 another term for Egyptian mongoose. – ORIGIN late 15th century (in ichneumon (SENSE 2)): via Latin from Greek ikhneumōn ‘tracker’, from ikhneuein ‘to track’, from ikhnos ‘track, footstep’.