non ‧ cha ‧ lant /ˈnɒnʃəl ə nt $ ˌnɑːnʃəˈlɑːnt/ BrE AmE adjective
[ Date: 1700-1800 ; Language: French ; Origin: Old French nonchaloir 'to pay no attention to' , from Latin calere 'to be warm' ]
behaving calmly and not seeming interested in anything or worried about anything:
‘Has he got a girlfriend?’ Jill asked, trying to sound nonchalant.
—nonchalance noun [uncountable]
—nonchalantly adverb :
He smiled nonchalantly.