-rd is added to numbers that end in 3, except those ending in 13, in order to form ordinal numbers such as 3rd or 33rd. 3rd is pronounced ‘third’.
...September 3rd 1990.
...the 33rd Boston Marathon.
...Canada’s 123rd birthday.
-RD
Meaning of -RD in English
Collins COBUILD Advanced Learner's English Dictionary. Английский словарь Коллинз COBUILD для изучающих язык на продвинутом уровне. 2006