iodine, iodin, I, atomic number 53 -- (a nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks))
one, 1, I, ace, single, unity -- (the smallest whole number or a numeral representing this number; "he has the one but will need a two and three to go with it"; "they had lunch at one")