noun which may take the genitive case particle 'no'
gentlemanly; gentlemanlike
Describes a person, behavior, or appearance that is refined, courteous, and dignified, like a gentleman. Often used with な or の.
I was impressed by his gentlemanly manner.
He attended the party in gentlemanly attire.
紳士的 is a more common na-adjective with a similar meaning, often used in phrases like 紳士的な態度 (gentlemanly attitude).
Compound of 紳士 (gentleman) + 風 (style/manner).