Guess the word by definition

12345678910
Across
  1. 2. feel, perceive
  2. 5. comfortable, easy to use
  3. 9. a gesture or symbol that indicates something
  4. 10. not to be sure of something
Down
  1. 1. the opposite of smart
  2. 3. the act of studying mathematics, physics and natural subjects
  3. 4. the person who does science
  4. 6. normal, average
  5. 7. something that is absurd
  6. 8. very big