The adjective has one meaning:

Meaning #1: disinclined to work or exertion
  Synonyms: faineant, indolent, lazy, otiose, work-shy, idle, indolent, lazy, shiftless, sluggard, sluggish. Informal do-nothing. Idioms: bone lazy.

Antonyms: active, diligent, energetic, hard-working, industrious, lively

slothfully sloth'ful·ly adv.
slothfulness sloth'ful·ness n

-Saturdays are often days when people feel lazy and relaxed.