IPA: /ˈbɔːrə/
KK: /ˈbɔroʊər/
A person or organization that takes something from someone else with the plan to give it back later.
The borrower promised to return the book next week.
Borrower → It is formed from "borrow" (from Old English "borgian", meaning to pledge or to lend) and "-er" (meaning a person who). A borrower is a person who pledges to return something that has been lent to them.
Think of someone who 'pledges' ('borgian') to return something they have 'borrowed' — that's what a borrower does.