by that means or because of that
"He knocked over the red wine, thereby ruining the table cloth"
By it; by that; by that means, or as a consequence of that.
"The company implemented stricter safety protocols, thereby reducing workplace accidents significantly."
In plain English: Thereby means that something happens as a direct result of what you just did.
"He turned off the lights, thereby saving electricity."
Usage: Use thereby to connect an action directly to its immediate result or the specific method used to achieve it. Place this word at the beginning of a clause following a comma to show how one event leads logically to another.
Thereby comes from Middle English therby, which was formed by combining "there" with "by." This construction has remained essentially unchanged in meaning since its origins in Old English.