internal angle vs interior angle

internal angle and interior angle both are nouns.

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

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

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

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