The best replacement for casual is formal.

The best alternatives to casual are rated as following:
★★★★★  formal
★★★★★  business casual
★★★  part time
★★  business professional
★★  ranked hearthstone
★★  casual
★★  causal
★★  dress shirt
★  smart casual
★  correlational
★  business dress
★  business attire
★  formal wedding
★  fine dining
★  business formal
★  permanent part time
★  saafir
★  formal attire
★  per diem
★  part time work
★  full time
★  gears of war 3
★  normal hon
★  part time jobs
★  dressy
  informal wedding dresses
  uniform
  college writing
  dress
  subscribed reddits
  committed relationship
  serious
  contractual
  formal dress code
  corporate casual
  professional
  college-level writing
  part time employment
  business
  fast food
  dressy casual
  semi-formal

Your alternative for casual is not listed? Suggest!
Speaking about casual, one probably shouldn't forget about tie.

Other search terms related to casual and their ratings are:
★★★★★ tie
★ suit
You have in mind a companion for casual and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of casual in all years. Click on graph for more.
casual
formal
business casual