Definition of "I" :

noun: the 9th letter of the Roman alphabet

noun: 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."

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)

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

"Ane' is Scottish."