I chose 'quench' because it's a medium difficulty word that meets all the criteria:
1. It's 6 letters long (between 4-10)
2. Uses only English letters
3. It's a real English word
4. Contains no spaces, hyphens, or special characters

It's moderately challenging because:
- Has the uncommon letter 'q'
- Contains the common letter cluster 'ch'
- Has a meaning familiar to most people (to satisfy thirst)
- Not an everyday word, but not extremely rare either