Broadband absorbers, capable of efficiently capturing solar energy across the full spectrum, are highly desired for solar-thermal applications. Here, we developed such an absorber by marriage of a high-entropy strategy and the prevailing spinel oxides. A high-entropy spinel oxide (CoCrFeMnNi)₃O₄ is synthesized by a facile sol-gel combustion approach. This high-entropy engineering narrows the band gap of the spinel oxide from 2.65 eV to 0 eV, showing a quasi-metallic characteristic. Notably, it reaches the lower limit for band gaps (0 eV) of spinel oxides, which has not been realized previously to the best of our knowledge. As a result, it leads to an impressive solar absorptance of 95.5% across the entire solar spectrum. As a proof of concept, we experimentally demonstrate its appealing potential in solar water evaporation, achieving an excellent evaporation efficiency of 96.5%. Our findings provide an avenue for the development of high-performance solar absorbers for high-efficiency solar-thermal conversion systems.