lepidopterous insect vs lepidopteran

lepidopterous insect and lepidopteran both are nouns.

Word	Noun	Adjective	Verb	Adverb
lepidopterous insect	Yes	No	No	No
lepidopteran	Yes	No	No	No

As nouns, lepidopterous insect and lepidopteran are synonyms defined as:

lepidopterous insect and lepidopteran: insect that in the adult state has four wings more or less covered with tiny scales

Other synonyms of lepidopterous insect include lepidopteron.

lepidopterous insect (noun)	lepidopteran (noun)
insect that in the adult state has four wings more or less covered with tiny scales	insect that in the adult state has four wings more or less covered with tiny scales