ad libitum vs spontaneously

ad libitum and spontaneously both are adverbs.

Word	Noun	Adjective	Verb	Adverb
ad libitum	No	No	No	Yes
spontaneously	No	No	No	Yes

As adverbs, ad libitum and spontaneously are synonyms defined as:

Other synonyms of ad libitum include ad lib, impromptu.

ad libitum (adverb)	spontaneously (adverb)
without advance preparation	in a spontaneous manner
	without advance preparation