slacker vs loafer

slacker and loafer both are nouns.

Word	Noun	Adjective	Verb	Adverb
slacker	Yes	No	No	No
loafer	Yes	No	No	No

As nouns, loafer is a hypernym of slacker; that is, loafer is a word with a broader meaning than slacker:

slacker: a person who shirks his work or duty (especially one who tries to evade military service in wartime)
loafer: person who does no work

Other hypernyms of slacker include bum, do-nothing, idler, layabout.

slacker (noun)	loafer (noun)
a person who shirks his work or duty (especially one who tries to evade military service in wartime)	person who does no work