/ ɪkˈspæns; NAmE / noun
expanse (of sth) a wide and open area of sth, especially land or water :
a wide / vast expanse of blue sky
flat expanses of open farmland
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WORD ORIGIN
mid 17th cent.: from modern Latin expansum something expanded, neuter past participle of expandere to spread out, from ex- out + pandere to spread.