Answer:
It cannot be seen, it weighs nothing, but when put into a barrel, it makes it lighter.
Add a T and I shoot through the sky. Then add an S and I multiply. What word is it?
This is needed both for courage and hardcover books.
I march before armies, a thousand salute me. My fall can bring victory, but no one would shoot me. The wind is my lover, one-legged am I. Name me and see me at home in the sky.
The higher I climb, the hotter I engage. I cannot escape from my crystal cage.
What never gets any wetter no matter how hard it rains?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?