Arbitrary: choose to, at will, because you wanted it that way, on a whim, with thought but little logic or reason Haphazardly: Without any thought or planning, carelessly, impulsively, "...you jumped right in". Arbitrary action, more then likely required some greater degree of thought then Haphazard action which could almost be considered 'reckless' Your sentence should be: "The boss 'arbitrarily' decided to give the office a day off" Hope this helped! =o)

Arbitrary refers to something chosen by some random preference. Haphazard means that something was chosen without any system and with disregard to safety and consequences. Haphazard is considered the more negative. An arbitrary choice can be made within some sort of plan - a haphazard choice would not. If I need someone to do a messy job, I might put all their names into a bowl and pick one. The choice would be arbitrary, but not haphazard. If I pick someone to to the same job and don't bother to find out the tools they need and make the choice suddenly at the last possible time, the choice is haphazard.