Just be aware that, though there is a "classical" form of the word, often there were through time and places variant spellings, due either to errors and decadence, as well to unavoidable variations such as one find between British and American English. But in general the safer form is that you find in most good and reliable dictionaries."Tesselae januam ornant."
Already from the fact that it's what mosaic pieces are called, it's apparent that it doesn't only mean “cube”, but also “a 4-corner rectangular piece, a square”. This is its primary meaning (τέσσαρες = 4), and cubes are called that by extension, since they're squares in 2D projection.Actually, “tessella” means “small cube”.
That r in Latin tended to assimilate, see eg. puella (from puerula) (girl), the feminine counterpart of puer (boy), also stella (star) from most likely sterula. Same here - was most likely tesserula at first before assimilating. The evolution was most likely -rula > -rla > -lla.Hi,
How come the diminutive of tessera 'square' is tessela 'small cube'? Why did the r disappear?