"The word "antimatter"... Strictly speaking, it's not... accurate... Antimatter is not "negative matter." It does not have negative mass, or negative spin, or negative (anti-) gravity (...scientists are... running experiments to see if antiprotons have the same kind of gravity as protons). ...One researcher has suggested replacing the... "anti-" with "co-,"... co-matter, co-protons,... Another... suggested... "exo-"... "Exo" in Greek means "outside." Other suggestions... "ob-" (obmatter, obproton) and "contra-" (contramatter and contraproton). None... ever caught on... Hannes Alfven in... Worlds-Antiworlds... said... let's coin a new word for "ordinary" matter... the word koinomatter... after the Greek word koinos, meaning common or well-known. ..."Matter will remain "matter" and "antimatter"... "antimatter"... However... "mirror matter" is the most accurate and unbiased term."