Nouns

(n)heaviness, weightinessthe property of being comparatively great in weight“the heaviness of lead”
(n)heavinesspersisting sadness“nothing lifted the heaviness of her heart after her loss”
(n)ponderousness, heavinessan oppressive quality that is laborious and solemn and lacks grace or fluency“a book so serious that it sometimes subsided into ponderousness”, “his lectures tend to heaviness and repetition”
(n)thickness, heavinessused of a line or mark
(n)burdensomeness, heaviness, onerousness, oppressivenessunwelcome burdensome difficulty