Nonchalant means casually indifferent or showing a cool lack of concern.
Nonchalant comes under adjective.
Synonyms: calm, casual, collected, composed, easygoing, relaxed, unexcited, unruffled.
Antonyms: affected, excited, moved, tense, concerned.
Your nonchalance may come back to hurt you. The board thinks you don't even want the promotion.
Ravi tried to act nonchalant when he walked past his ex-girlfriend, but he was so uptight that he tripped and spilled hot chocolate all over himself.