blithe

adjectives

lacking or showing a lack of due concern
"spoke with blithe ignorance of the true situation"
is similar to
lacking in interest or care or feeling
"the average American...is unconcerned that his or her plight is the result of a complex of personal and economic and governmental actions...beyond the normal citizen's comprehension and control"; "blithely unconcerned about his friend's plight"
carefree and happy and lighthearted
"was loved for her blithe spirit"; "a merry blithesome nature"; "her lighthearted nature"; "trilling songs with a lightsome heart"
is derived from