Antonyms of adj mournful

2 senses of mournful

Sense 1
mournful, plaintive -- (expressing sorrow)

INDIRECT (VIA sorrowful) -> joyful -- (full of or producing joy; "make a joyful noise"; "a joyful occasion")

Sense 2
doleful, mournful -- (filled with or evoking sadness; "the child's doleful expression"; "stared with mournful eyes"; "mournful news")

INDIRECT (VIA sad) -> glad -- (showing or causing joy and pleasure; especially made happy; "glad you are here"; "glad that they succeeded"; "gave a glad shout"; "a glad smile"; "heard the glad news"; "a glad occasion")

Similarity of adj mournful

2 senses of mournful

Sense 1
mournful, plaintive -- (expressing sorrow)
       => sorrowful (vs. joyful) -- (experiencing or marked by or expressing sorrow especially that associated with irreparable loss; "sorrowful widows"; "a sorrowful tale of death and despair"; "sorrowful news"; "even in laughter the heart is sorrowful"- Proverbs 14:13)

Sense 2
doleful, mournful -- (filled with or evoking sadness; "the child's doleful expression"; "stared with mournful eyes"; "mournful news")
       => sad (vs. glad) -- (experiencing or showing sorrow or unhappiness; "feeling sad because his dog had died"; "Better by far that you should forget and smile / Than that you should remember and be sad"- Christina Rossetti)