longicorn adjective 2noun 2forms 1 adjective2 •Long-horned. •(no longer used) Of or relating to the former taxonomic insect group Longicorniahttps://www.merriam-webster.com/dictionary/Longicornia, encompassing numerous beetles with long antennae. Some are now classified as Cerambycidae (longhorn beetles). noun2 •(old-fashioned) Synonym of longhorn beetle. •(no longer used) One of the Longicorniahttps://www.merriam-webster.com/dictionary/Longicornia, a former taxonomic insect group of long-horned beetles. formslongicorns