I chose 'quench' because:
1. It's 6 letters long (within 4-10 range)
2. Contains only standard English letters
3. It's a medium difficulty word:
   - Has uncommon letter 'q'
   - Contains common letters 'n', 'e'
   - Not used very frequently in daily conversation
   - But still a familiar concept (quench thirst)
4. It's a real English word (verb)
5. No special characters, spaces, or hyphens
This word will give the opponent a good challenge while still being guessable.