offhanded vs ad-lib

offhanded is not a noun while ad-lib is a noun.

Word	Noun	Adjective	Verb	Adverb
offhanded	No	Yes	No	Yes
ad-lib	Yes	Yes	Yes	No

As adjectives, offhanded and ad-lib are synonyms defined as:

Other synonyms of offhanded include extemporaneous, extemporary, extempore, impromptu, off-the-cuff, offhand, unrehearsed.

offhanded (noun)	ad-lib (noun)
	remark made spontaneously without prior preparation

offhanded (adjective)	ad-lib (adjective)
casually thoughtless or inconsiderate	with little or no preparation or forethought
with little or no preparation or forethought	said or done without having been planned or written in advance

offhanded (verb)	ad-lib (verb)
	perform without preparation

offhanded (adverb)	ad-lib (adverb)
in a casually inconsiderate manner
without previous thought or preparation