tettigoniid vs katydid

tettigoniid and katydid both are nouns.

Word	Noun	Adjective	Verb	Adverb
tettigoniid	Yes	No	No	No
katydid	Yes	No	No	No

As nouns, katydid is a hyponym of tettigoniid; that is, katydid is a word with a more specific, narrower meaning than tettigoniid:

tettigoniid: grasshoppers with long threadlike antennae and well-developed stridulating organs on the forewings of the male
katydid: large green long-horned grasshopper of North America; males produce shrill sounds by rubbing together special organs on the forewings

Other hyponyms of tettigoniid include Jerusalem cricket, sand cricket, Stenopelmatus fuscus.

tettigoniid (noun)	katydid (noun)
grasshoppers with long threadlike antennae and well-developed stridulating organs on the forewings of the male	large green long-horned grasshopper of North America; males produce shrill sounds by rubbing together special organs on the forewings