The Chinese idiom "无济于事" is formed by sequentially combining the characters 无 (meaning "not" or "without"), 济 (meaning "to help" or "aid"), 于 (a preposition meaning "to" or "in"), and 事 (meaning "matter" or "affair"), resulting in a literal composition that translates to "not helping to the matter", thereby expressing the concept of being useless or ineffective.