"Eleventh" is the Engpsh word for "第十一". Here is an example sentence using "eleventh":

"Today is the eleventh day of the month."

In addition, "11th" is often used as an abbreviation for "eleventh", as in:

"The concert is on the 11th of next month."

Note that when saying or writing the number "11" in Engpsh, it is pronounced as "eleven", not "one-one".