שׁבת shbt verb: "rest, stop [doing something]" the hiphil means "cause to stop, end, destroy, exterminate" in Am 8:4 the notion seems to be that the actions of the rich are exterminating the poor. This word is chosen partly for the echo it finds in the next verse which quotes them as wishing the Sabbath were over.

שַׁבָּת shbt noun: "Sabbath" the seventh day of the week, when God ceased creating (Gen 2:1-3) and humans rest and worship. In Am 8:5 the rich merchants are impatient for the rest day to be over so they can start selling again.