insouciant
definition
casual lack of concern or indifference
example
Despite the looming deadline, she remained insouciant about her project, confident that everything would work out in the end.
synonyms
carefreenonchalantunconcerned
word origin — French, from 'insouciant' meaning 'not caring' (in- 'not' + 'souciant' from 'souci' meaning 'trouble')