1. In a mirthful manner.

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

• turthfully,
• mirthfull,
• nirthfully,
• kirthfully,
• jirthfully,
• murthfully,
• mjrthfully,
• mkrthfully,
• morthfully,
• m9rthfully,
• mirthfilly,
• mirtfully,
• mirthflly,
• mirthfuly,
• mirhtfully,
• mirthfullyy,
• myrthfully,
• rithfully,
• mirthfulyy,
• worthfullly

• mirthful,
• mirthfulness.

The adjective form of "mirthfully" is "mirthful".

The plural form of "mirthfully" remains the same, as it is an adverb and does not change when pluralized.

The singular form of the word "mirthfully" is "mirthful"