slacken off vs ease off

slacken off and ease off both are verbs.

Word	Noun	Adjective	Verb	Adverb
slacken off	No	No	Yes	No
ease off	No	No	Yes	No

As verbs, slacken off and ease off are synonyms defined as:

Other synonyms of slacken off include ease up, flag.

slacken off (verb)	ease off (verb)
become less intense	become less intense
	reduce pressure or intensity