They re-mortgaged their apartment to renovate the kitchen.

re-mortgaged 是动词 re-mortgage 的过去式。re-mortgage 由前缀 re-（表示"再次"）和动词 mortgage（抵押）组成，字面意思是"再次抵押"，指对已经抵押过的房产进行第二次抵押贷款。