I do not recall any Hebrew word for sphere. I will check my Hebrew dictionary at home, though if there is a word, it may well be a twentieth-century coinage. (Modern Israeli Hebrew includes many words that did not exist in the Bible, but which were usually formed from Biblical roots. The word for "computer", for example, comes from the root meaning "to think"; the word "railroad" comes from a root meaning "to ride").
The verse in Isaiah speaking of "the circle of the earth" uses the word chug, which usually means a disc or ring.
The verse in Isaiah speaking of "the circle of the earth" uses the word chug, which usually means a disc or ring. A couple of years ago when that same verse came up, I found an on-line concordance, which not only gives the word's meaning, but it also cites all the other verses where that same word appears. As I recall, the word is never used in the context of a sphere.
The word for "computer", for example, comes from the root meaning "to think"; the word "railroad" comes from a root meaning "to ride"). Irish does the same sort of thing; unfortunately, Irish, unlike Hebrew, is a dying language.