/ ˈnɒnʃələnt; NAmE ˌnɑːnʃəˈlɑːnt/ adjective
behaving in a calm and relaxed way; giving the impression that you are not feeling any anxiety
SYN casual :
to appear / look / sound nonchalant
'It'll be fine,' she replied, with a nonchalant shrug.
► non·cha·lance / -ləns; NAmE -ˈlɑːns/ noun [ U ]:
an air of nonchalance
► non·cha·lant·ly adverb :
He was leaning nonchalantly against the wall.
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WORD ORIGIN
mid 18th cent.: from French , literally not being concerned, from the verb nonchaloir .