adjective
Thirtieth.
The correct spelling for 30th is "thirtieth".
"not thirtieth." There really isn't a precise single-word antonym for it.
The correct term is "thirtieth" when referring to the ordinal number that comes after the twenty-ninth. It is used in contexts such as dates (e.g., "the thirtieth of the month") or to describe a position in a sequence. "30th" is simply a numerical representation of "thirtieth."
The thirtieth sultan of the Ottoman Empire was Mahmud II.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.