1. In a mysterious manner.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• mysteroiusly,
• mysteriosly,
• mysteryously,
• mysteriouse,
• misteriosly,
• misteriusly,
• mysteriosuly,
• mysterioulsy,
• mysterously,
• myseriously,
• misteriously,
• mysteriouss,
• misterously,
• myseteriously,
• mysteriousely,
• mysteriusly,
• mysteriouslyy,
• misteuriously,
• mistariously,
• mystiriously

• mystery novel,
• mysterious,
• mystery story.

The adjective form of the word "mysteriously" is "mysterious".

The plural form of the word "mysteriously" remains the same, as it does not change in plural form.

The singular form of the word "mysteriously" is "mysterious"