spontaneous vs unwritten

spontaneous and unwritten both are adjectives.

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

As adjectives, spontaneous and unwritten are synonyms defined as:

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

Other synonyms of spontaneous include ad-lib.

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