(real estate) key money: an amount of money paid to a landlord to start a lease agreement, usually non-refundable and separate from the deposit, and often a set multiple of the monthly rent amount

apartment

apartment building, apartment house

needed, necessary

need, necessity

apartment building (abbr. アパート)

necessity (quality or state of being necessary, unavoidable, or absolutely requisite)

unnecessary

needlessness

necessary evil