Slight and small are synonyms for frivolous. Sensible is the opposite of frivolous. We have given below a collection of synonyms for "frivolous".
Trivial behaviours and things are not only of minimal value but are usually very silly and purposeless and are a waste of time, energy, and effort compared to common sense. One must be smart and cautious of anyone who has no serious purpose or value. For example, he was incredibly frivolous, passive and indifferent; his father had given it to him. If we were playing for money, I'm sure you wouldn't be so frivolous.