"spaciousness" in the noun sense
1. capaciousness, roominess, spaciousness, commodiousness
spatial largeness and extensiveness (especially inside a building
"the capaciousness of Santa's bag astounded the child"
"roominess in this size car is always a compromise"
"his new office lacked the spaciousness that he had become accustomed to"
Source: WordNet® (An amazing lexical database of English)
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