shirking vs slacking

shirking and slacking both are nouns.

Word	Noun	Adjective	Verb	Adverb
shirking	Yes	No	No	No
slacking	Yes	No	No	No

As nouns, shirking and slacking are synonyms defined as:

Other synonyms of shirking include goldbricking, goofing off, soldiering.

shirking (noun)	slacking (noun)
the evasion of work or duty	the evasion of work or duty