Princeton's WordNet

1. 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:
   different, definite, comparable, ordinary, divided, ordinal, uncombined

2. one(adj)

   a single person or thing

   Synonyms:
   unity, ace, single

   Antonyms:
   different, divided, definite, ordinary, comparable, ordinal, uncombined

3. 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:
   ordinary, definite, different, uncombined, ordinal, comparable, divided

4. one(a), unitary(adj)

   having the indivisible character of a unit

   Antonyms:
   definite, ordinary, different, uncombined, divided, comparable, ordinal

5. one(a)(adj)

   of the same kind or quality

   Antonyms:
   ordinal, different, divided, uncombined, definite, comparable, ordinary

6. one(a)(adj)

   used informally as an intensifier

   Antonyms:
   divided, ordinal, comparable, definite, different, ordinary, uncombined

7. one(a)(adj)

   indefinite in time or position

   Antonyms:
   ordinal, different, divided, uncombined, ordinary, definite, comparable

8. one(adj)

   being a single entity made by combining separate components

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

   Antonyms:
   ordinary, definite, ordinal, divided, uncombined, comparable, different

9. matchless, nonpareil, one(a), one and only(a), peerless, unmatched, unmatchable, unrivaled, unrivalled(adj)

   eminent beyond or above comparison

   Antonyms:
   ordinal, ordinary, definite, divided, uncombined, comparable, different