Answer:
As a stone inside a tree, I’ll help your words outlive thee. But if you push me as I stand, the more I move the less I am.
Sometimes I fly as fast as the speed of light. Sometime I crawl as slow as a snail. Unknown until I am measured but you will certainly miss me when I’m gone.
I no longer have eyes, but once I did see. Once I had thoughts, but now I’m white and empty. What am I?
I am a portal to another world which you cannot enter. Only you can see me but I can't see you.
The letter S is added to pluralise most words in the English language. eg. Letter to Letters Word to Words and Language to Languages. But I am a word that is pluralised with the addition of the letter C.
As round as an apple. As deep as a cup. All the king's horses can't pull it up.