slacking vs shirking

slacking and shirking both are nouns.

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

As nouns, slacking and shirking are synonyms defined as:

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

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