The Hebrew is “shamayim”, which break down as “sham” (rhymes with ‘palm’) meaning “there” and “mayim” (rhymes with “buy’em") meaning “water”.
I presume this is a traditional rabbinical interpretation; it is certainly not an actual etymology (cf. Ugaritic shmm, Akkadian shamu ‘rain,’ plural ‘heaven’; there are also cognates in Aramaic, Arabic, and South Arabic).
LH, you are correct, as usual, but I believe that citing the cognates only removes the question by one step. E.g, the Assyrian word for “heavens” is “shammu”, but the word for water is “mu”. Same with Aramaic: the word for heaven is “shamaya” and the word for water is “maya.” As far as I can detect from by BDB, “sham” in those languages means “there.” BDB also lists “sham” (there) at the end of its entry on “shamayim” pg. 1030, left column, at the bottom in what I think is the standard edition.
I would same the same to the other posts: we can translate “shamayim” conceptually as heaven(s) or lofty, but my admittedly limited exposure to Assyrian, Akkadian, Ugaritic, etc. ( I don’t read the alphabet, but look up the words in Hebrew or English transliteration), tells me that it is plausible beyond rabbinic Midrash that the etymology I offered is reasonable.
I should have offered it, however, it in more caution terms.
On rakia: in the verbal forms in Hebrew, raka’ means to stretch out, and rike’a means more to hammer out, flatten out or make shallow. Hirkiya’ does not add much to either of those meanings. The glass bowl image offered would come closest, in my opinion.