10+ advanced American English words!

1. **Mellifluous:** Sweet or musical; pleasant to hear. 2. **Ephemeral:** Lasting for a very short time. 3. **Quixotic:** Extremely idealistic; unrealistic and impractical. 4. **Obfuscate:** To deliberately make something unclear or difficult to understand. 5. **Serendipity:** The occurrence and development of events by chance in a happy or beneficial way. 6. **Ubiquitous:** Present, appearing, or found everywhere. 7. **Ineffable:** Too great or extreme to be expressed or described in words. 8. **Lethargic:** Characterized by a lack of energy or enthusiasm. 9. **Pernicious:** Having a harmful effect, especially in a gradual or subtle way. 10. **Sycophant:** A person who acts obsequiously toward someone important in order to gain advantage.