A mortgage is a loan in which the lender may use your property as payment if you don't pay back the loan. Offer your friend a mortgage for the $20 he wants . . . with his bike as security.
Most people obtain a mortgage when they buy a house. The bank extends the loan because of the guarantee that the house will be the bank’s to sell if the debt isn’t repaid. When you make this deal, you have mortgaged your house — the word mortgage can be used as a noun or a verb.