Ice
Ice
Gem.
Gem, perhaps?
tree
One possibility is the word diamond. Diamonds are the hardest substance in the world.
There isn't one that begins with an 'S' A three letter word for an evergreen tree is fir.
Maple.
tree
ElmOak
The main stem of a tree is the 4-letter word bole. The word is a noun and is another word for truck.
pine
Tree