noun
Used to describe items, facilities, or services intended for men, often with a refined or formal nuance from 紳士 (gentleman). Common in product labels, signs, and descriptions.
この店には紳士用のアクセサリーが豊富にあります。
This store has a wide selection of men's accessories.
紳士用トイレは二階にございます。
The gentlemen's restroom is on the second floor.
男性用 is a more general term for 'for men' without the gentlemanly nuance; 紳士用 sounds more refined or formal.
Compound of 紳士 (gentleman) + 用 (for use). The term likely emerged in the early 20th century as Western-style goods and facilities became common, using 紳士 to convey a sense of refinement.