1. Calmly.

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

• serenty,
• sertanely,
• serrnly,
• serentiy,
• certenely,
• cerently,
• sereasly,
• strenly,
• sertenly,
• serinly,
• serenety,
• serevely,
• sereusly,
• sereisly,
• sereneity,
• surently,
• serenly,
• sernely,
• serenley,
• seranely

The adjective form of the word "serenely" is "serene".

The plural form of the word "serenely" is "serenely." It is an adverb, and adverbs generally don't have plural forms.

The singular form of the word "serenely" is "serene"