interior angle vs internal angle

interior angle and internal angle both are nouns.

Word	Noun	Adjective	Verb	Adverb
interior angle	Yes	No	No	No
internal angle	Yes	No	No	No

As nouns, interior angle and internal angle are synonyms defined as:

interior angle and internal angle: the angle inside two adjacent sides of a polygon

interior angle (noun)	internal angle (noun)
the angle inside two adjacent sides of a polygon	the angle inside two adjacent sides of a polygon