nonchalant
adjective /ˈnɒnʃələnt/
  /ˌnɑːnʃəˈlɑːnt/
- behaving in a calm and relaxed way; giving the impression that you are not feeling worried synonym casual (2)- to appear/look/sound nonchalant
- ‘It'll be fine,’ she replied, with a nonchalant shrug.
 Extra Examples- She was almost nonchalant about the dangers involved.
- ‘They're not back yet then?’ She tried to sound nonchalant.
- He tried to appear nonchalant about the risks he was taking.
- She gave a nonchalant shrug.
 Oxford Collocations DictionaryNonchalant is used with these nouns:- attitude
- shrug
 Word Originmid 18th cent.: from French, literally ‘not being concerned’, from the verb nonchaloir.