Definition, synonyms and related words
By what, in which direction; how.
"The new law was designed whereby citizens could vote from home without leaving their neighborhoods."
In plain English: Whereby is an old-fashioned word used to explain how something happens as a result of another action.
"The system works whereby users can log in with their social media accounts."
Whereby is a compound word formed from where and by. It entered English as a single adverbial unit meaning "through which."