かさむ
かさむ · kasamu · JLPT N1 · noun
to pile up
📚 かさ (嵩, bulk or volume) + む verb ending = to grow in bulk, so costs pile up
The noun かさ (嵩) means bulk or volume, and the verb ending む turns it into 'to become bulky.' Expenses かさむ when the total keeps growing, and stacks かさむ as they get taller.