adjective

1. of little value or importance; trifling; trivial
2. not properly serious or sensible; silly and light-minded; giddy a frivolous remark, a frivolous youth
3. having no basis in law because of the lack of sound legal arguments, facts, etc. or not brought to court in good faith

Etymology: ME < frivol (< OFr frivole < L frivolus, fragile, silly, akin to friare: see friable) + -ous