To enlarge on what Citrange said --

Of course the trees don't care what you call them, and grocery stores don't much care either. But if you're looking in "official" literature for information, it helps to have the spellings right, since that makes it easier to find information on the correct fruit. So for the record (not picking on anybody here):

pummelo = shaddock = Citrus grandis = Citrus maxima

pomelo = grapefruit = Citrus paradisi. (almost certainly a hybrid of pummelo by some other citrus)

"Pomelo" is being misused by the grocery store. And I don't believe "pomello" or "pommelo" are standard spellings for any fruit.