General:
* Grand: This is the most common and general opposite of "petit" (small). It can be used for both size and importance.
Specific to size:
* Gros: This translates to "big" or "large" and specifically refers to physical size.
* Énorme: This translates to "huge" or "enormous" and emphasizes a significant size.
Specific to importance:
* Important: This translates to "important" and is the opposite of "petit" when referring to significance.
Specific to quantity:
* Beaucoup: This translates to "many" or "a lot" and is the opposite of "petit" when referring to quantity.
The best word to use will depend on the specific situation.