sorrowful has no recorded synonym. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is joyful.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
experiencing or marked by or expressing sorrow especially that associated with irreparable loss
“sorrowful widows”
Synonyms, antonyms and the broader and narrower relations for sorrowful come from Princeton University’s WordNet. Full sources and licences.