Answer:
A single syllable do I claim black was my most famous name; Fetal to mortals here below thousands have I slain in a single blow.
The more you have of it the less you see. What is it?
I begin with the letter āiā, if you add āaā in front of me, I become a new word with a different meaning, but still sounds exactly the same. What word am I?
I start with āeā end with āeā. I have whole countries inside me. What am I?
I'm found in socks ties and hands. What am I?
Give it food and it will live, give it water and it will die.