a.
1.
Senseless, witless, stupid, foolish, simple, weak, childish, inept, weak-minded, brainless, shallow.
2.
Absurd, trifling, frivolous, extravagant, preposterous, nonsensical, unwise, indiscreet, imprudent.
SILLY
Meaning of SILLY in English
Soule. Dictionary of English synonyms. Словарь английских синонимов. 2012