Here's why:
* "Steal" is a verb, meaning to take something without permission.
* "Stealth" is a noun, referring to the act of moving or operating secretly, or the quality of being done secretly.
While both words are related to the idea of secrecy and taking something without being noticed, they are distinct words with different meanings.
Here are some examples:
* Steal: The thief tried to steal the jewels.
* Stealth: The spy used stealth to infiltrate the enemy base.
The abstract noun for "steal" is "theft". Theft refers to the act of stealing itself, considered as a concept or idea.