Use the adverb nonchalantly to describe an action done in a really relaxed, casual, unconcerned way. From now on if someone asks you to define the word nonchalantly, you can do it . . . nonchalantly. It’s no big deal!
You may nonchalantly hit a 3-point shot during the game — you've done it a million times before so you're relaxed and confident. Nonchalantly can also describe something that just seems relaxed. Even if you’re truly stressed out about an upcoming test, you can still shrug nonchalantly about it to make people think you’re unconcerned.