Correct spelling

33rd

Correct spelling, explanation: suffix -rd is used for ordinal numbers which include number 3 at the end, for example 103rd, 43rd, 33rd (13th as a separate number is an exception). -th is a usual suffix, but -rd, -st and -nd are exceptions for numbers 1, 2 and 3. Therefore 33rd is the correct form and 33th is wrong.

Definition of 33rd:
numeral, ordinal number between 32nd and 34th
Sally is really stubborn – this is her 33rd try in getting a driving licence and she is still trying!
His 33rd birthday party was wild.


Incorrect spelling

33th

Incorrect spelling, explanation: this form is incorrect as the suffix for ordinal number 3 and every number ending with 3 is -rd, -th is a suffix for most numbers, however 3 is one of the exceptions. Therefore 33th is a wrong form and the correct one is 33rd.

Incorrect spelling

33nd

Incorrect spelling

Incorrect spelling

33st

Incorrect spelling