let off vs exempt

let off is not an adjective while exempt is an adjective.

Word	Noun	Adjective	Verb	Adverb
let off	No	No	Yes	No
exempt	No	Yes	Yes	No

As verbs, let off and exempt are synonyms defined as:

Other synonyms of let off include excuse, relieve.

let off (adjective)	exempt (adjective)
	(of persons) freed from or not subject to an obligation or liability (as e.g. taxes) to which others or other things are subject
	(of goods or funds) not subject to taxation

let off (verb)	exempt (verb)
grant exemption or release to	grant exemption or release to
	grant relief or an exemption from a rule or requirement to