IPA: /ˈmɪʃ.ə.vəs.li/
KK: /ˈmɪs.tʃə.vəs.li/
In a way that shows a playful desire to cause trouble or annoy someone.
The child smiled mischievously as he planned his next prank.
Mischievously → It is formed from "mischief" (from Old French *meschief*, meaning misfortune or harm) and the suffix "-ously" (meaning in a manner of). The word "mischievously" describes acting in a manner that causes mischief or playful trouble.
Think of 'mischief' as causing playful trouble, and remember that 'mischievously' means doing so in a manner that is playful and troublesome.