insane adjective Stress: second syllable 🤍 Save Syllables: in-sane (2) English Definition Mentally ill or extremely foolish. Example Sentence Spending that much money was an insane decision. US IPA /ɪnˈseɪn/ 🔊 Listen US UK IPA /ɪnˈseɪn/ 🔊 Listen UK Synonyms mad crazy lunatic foolish wild Antonyms sane rational sensible Share this Word Facebook WhatsApp X Telegram Copy Link