Princeton's WordNet

1. iodine, iodin, I, atomic number 53(noun)

   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)

   Synonyms:
   tincture of iodine, iodin, unity, single, iodine, atomic number 53, one, ace

   Antonyms:
   ordinal

2. one, 1, I, ace, single, unity(noun)

   the smallest whole number or a numeral representing this number

   Synonyms:
   virtuoso, star, angiotensin-converting enzyme, bingle, single, champion, superstar, unity, mavin, wholeness, maven, ace, oneness, one, sensation, genius, integrity, hotshot, wiz, whiz, atomic number 53, iodin, adept, wizard, angiotensin converting enzyme, iodine, whizz

   Antonyms:
   ordinal

3. I, i(adj)

   the 9th letter of the Roman alphabet

   Synonyms:
   iodin, one, iodine, unity, ace, atomic number 53, single

   Antonyms:
   ordinal

4. one, 1, i, ane(adj)

   used of a single unit or thing; not two or more

   Synonyms:
   unitary, unrivalled, one(a), i, peerless, matchless, unmatchable, unmatched, unrivaled, nonpareil, one and only(a), one, ane

   Antonyms:
   ordinal