a.
1.
Senseless, idiotic, silly, weak, daft, simple, irrational, insensate, shallow, brainless, witless, thick-skulled, buffle-headed, shallow-brained.
2.
Unwise, unreasonable, absurd, ridiculous, nonsensical, ill-judged, preposterous, indiscreet, imprudent.
3.
Idle, trivial, trifling, vain, childish, puerile, contemptible.