The adverb blithely describes something you do in a casually cheerful, somewhat neglectful way, like when you blithely ride your bike down the street, not even thinking about all the homework you have to do.

Something that's done blithely is careless, like a group of kids blithely dashing off across a frozen pond on their ice skates, forgetting about their slower friend. You could talk blithely about your brand new laptop, forgetting that your friend can't afford a new computer. Blithely also means "happily," without implying that anything is being overlooked or ignored, like a winning team blithely celebrating their victory.

Definitions of blithely

adv in a joyous manner

gayly, happily, jubilantly, merrily, mirthfully
in an unpleasant way

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