unwritten vs spontaneous

unwritten and spontaneous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unwritten	No	Yes	No	No
spontaneous	No	Yes	No	No

As adjectives, unwritten and spontaneous are synonyms defined as:

unwritten and spontaneous: said or done without having been planned or written in advance

Other synonyms of unwritten include ad-lib.

unwritten (adjective)	spontaneous (adjective)
based on custom rather than documentation	happening or arising without apparent external cause
using speech rather than writing	said or done without having been planned or written in advance
said or done without having been planned or written in advance