I chose 'quench' because:
1. It's 6 letters long (within the 4-10 letter requirement)
2. Contains only English letters
3. It's a medium difficulty word:
   - Has the uncommon letter 'q'
   - Contains 'ch' combination
   - Not used extremely frequently in daily conversation
   - But still a familiar concept (quench your thirst)
4. It's a real English word (verb)
5. No special characters, spaces, or hyphens