General:
* Wood: A small forest, especially of trees of a particular kind.
* Copse: A small group of trees.
* Thicket: A dense growth of bushes or small trees.
* Stand: A group of trees, especially one planted for a specific purpose.
* Plantation: A large area of land planted with trees, especially for commercial purposes.
More specific:
* Orchard: A piece of land planted with fruit trees.
* Arboretum: A place where trees are grown for scientific or educational purposes.
* Oaks: A grove specifically of oak trees.
* Palm grove: A grove of palm trees.
The best synonym depends on the specific type of trees and the overall feel of the grove you're describing.