external vs extraneous

external is a noun but extraneous is not a noun.

Word	Noun	Adjective	Verb	Adverb
external	Yes	Yes	No	No
extraneous	No	Yes	No	No

As adjectives, external and extraneous are synonyms defined as:

Other synonyms of external include outside.

external (noun)	extraneous (noun)
outward features

external (adjective)	extraneous (adjective)
happening or arising or located outside or beyond some limits or especially surface	not belonging to that in which it is contained; introduced from an outside source
coming from the outside	not pertinent to the matter under consideration
from or between other countries	coming from the outside
purely outward or superficial	not essential