Synonyms for Heaviness (same or very similar meaning)
WordNet sense 1 (an oppressive quality that is laborious and solemn and lacks grace or fluency):
ponderousness
WordNet sense 2 (used of a line or mark):
thickness
WordNet sense 3 (the property of being comparatively great in weight):
weightiness
WordNet sense 4 (unwelcome burdensome difficulty):
onerousness, oppressiveness, burdensomeness
From the ODE community, based on WordNet
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