Back to the question.
I thought that they were called "tanks" because when they arrived at the front in ww1 some of the brits thought they looked like water tanks and the name just stuck.
But when you think about it the name seems to fit almost all armored vehiciles.
From a Whippet to a Char B,or a Semovente to a Merkava.
No matter what it is ,its still a tank.