Synonyms for Mournful (same or very similar meaning)
WordNet sense 1 (expressing sorrow):
plaintiveWordNet sense 2 (experiencing or marked by or expressing sorrow especially that associated with irreparable loss):
sorrowfulWordNet sense 3 (filled with or evoking sadness):
dolefulWordNet sense 4 (experiencing or showing sorrow or unhappiness):
sadFrom the ODE community, based on WordNetadd/edit