From Multinary Solid Solutions to High-Entropy Nanomaterials

High-entropy nanomaterials (HENMs)─nanoscale solid solutions containing multiple principal elements in near-equiatomic ratios─have rapidly evolved from early multinary alloys into a broadly tunable platform spanning alloys, oxides, sulfides, and emerging ceramics such as carbides, nitrides, phosphides, and fluorides. This perspective maps that evolution across compositional expansion, dimensional reduction, and structural diversification (solid, hollow, mesoporous, and layered architectures). We synthesize current knowledge of the thermodynamic and kinetic principles that govern phase formation and metastability at the nanoscale, emphasizing the roles of configurational entropy stabilization versus enthalpy penalties, sluggish diffusion, and rapid quenching. Top-down and bottom-up routes are critically assessed, highlighting how far-from-equilibrium pathways enable homogeneous multielement mixing at the nanoscale. We further highlight high-throughput pipelines that couple continuous synthesis with rapid electrochemical mapping, and machine-learning frameworks that compress the combinatorial search space and reveal composition-structure-property rules. Finally, we outline key challenges and opportunities in component space expansion, predictive synthesis control, operando/high-throughput characterization, interpretable machine learning, device-level integration, and resource sustainability. Together, these advances facilitate the transition from "entropy-stabilized curiosities" to engineered HENMs with programmable performance for catalysis, energy conversion/storage, electronics, and extreme-environment technologies.