Busy / Busyness / Business
The word business originally comes from the English adjective busy.
In English, many adjectives become nouns when the suffix -ness is added.
Here are some common examples:
Today the word business refers to employment or the action of engaging with others in commerce. However, the original uses of this word referred to actually being busy. This makes sense, doesn't it. If someone has a job, wouldn't they be busy? In addition, 'busiless' was once used to refer to someone at leisure or unemployed. This is not commonly used today.
The adjective busy and the suffix -ness form the word business. To avoid confusion about meaning, the word busyness, spelled with y instead of i, is used as a noun to mean simply being busy.
Think about this the next time you hear someone ask, "How's business?"