The Latin for heaven was caelum normally. The Latin Dictionary and Grammar Aid http://www.nd.edu/~archives/latgramm.htm gives for coel- see cael-. ae, pronounced [eye] and oe, pronounced [oy] both went to e in medieval Latin and followed the rule that turned a c from a hard [k] sound to a soft sound, [ch] in Italianate Church Latin or [ts] in German Church Latin. This sound became the [s] sound in various non-liturgical Latins, of which scientific is one.

This notwithstanding, the AHD gives the etymology Greek koilos, hollow, + Greek akantha, spine, through the Modern Latin Coelacanthus. I have found no evidence that the Greek koilos ever produced anything in Classical or Medieval Latin unless some blasphemous 12th century monk editorialized caelum to coelum to indicate his belief that the concept of heaven was a hollow mockery.

What this long winded diatribe comes down to is another vote for [see luh canth].