Sub, Super

12345678
Across
  1. 2. One who oversees tasks and ensures rules are followed
  2. 4. To yield to authority or turn in something officially
  3. 5. So good, it's nearly flawless
  4. 6. It dives deep yet never gets wet on the inside
  5. 7. Describes something of higher quality or greater importance
  6. 8. It runs beneath the city but never sees the sun
Down
  1. 1. To sink below the surface, especially in liquid
  2. 3. To gradually diminish, like fear or floodwaters
  3. 4. Beyond natural strength or endurance
  4. 7. Speed that breaks sound barriers