I in WordNet English dictionary

1. 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"
   one  1  I  ace  single  unity 
   
2. 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)
   iodine  iodin  I  atomic number 53 
   
3. the 9th letter of the Roman alphabet
   I  i 
   
4. the 9th letter of the Roman alphabet
   I  i