LEND is a verb meaning “give something to someone for a short time, expecting that you will get it back.”
BORROW is a verb meaning, “get something from someone, intending to give it back after a short time.”
When you give something, you LEND it; when you get or receive something, you BORROW it. “Borrow” and “lend” are reciprocal. You LEND a person a book. That someone is BORROWING it from you.
“Lend” is what the person who gives the book does, and “borrow” is what the person who receives the book does.
lend —-> (TO) someone
someone —-> borrow (FROM)
Hansel will LEND $1000.00 to Gretel.
Gretel will BORROW $1000.00 from Hansel.
“Lend and borrow” are a verb pair, much like “send and receive,” “offer and accept,” and “sell and buy.” You can’t substitute one for the other; one gives, one receives. They have opposite meanings that correspond to giving and taking, respectively.