重さ is read as おもさ (omosa) and means weight.
おもさ
omosa
じゅうたい
serious condition
じゅうだい
serious
おもみ
weight
かさねる
to repeat many times over
じゅうりょく
gravity
じゅうしん
(one's) balance
おもい
heavy
じゅうこうぎょう
heavy industry
おもんじる
to respect
かさなる
to be piled up
じゅうびょう
serious illness
おも
main secondary or supporting role (in kyogen)