adjective
Thirtieth.
The correct spelling for 30th is "thirtieth".
"not thirtieth." There really isn't a precise single-word antonym for it.
The part of speech for this particular word is a noun.
part of speech
The thirtieth sultan of the Ottoman Empire was Mahmud II.
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.
The part of speech for "rapid" is an adjective.