They decided to re-mortgage their house to get a better interest rate.

re-mortgage 由前缀 re-（表示“重新”）和 mortgage（抵押贷款）组成，字面意思是“重新抵押”。re-mortgage 指对已有抵押贷款的房产再次进行抵押，通常是为了获得更优惠的贷款条件或提取资金。