noun which may take the genitive case particle 'no'
top-notch; first-rate; leading
Describes something of the highest quality or rank, often used for products, services, or people. Functions as a no-adjective modifying a noun.
彼は一線級のエンジニアだ。
He is a top-notch engineer.
このホテルは一線級のサービスを提供
This hotel provides first-rate service.