"Third" how to spell?
There is a rule in the Russian language, through which you can learn how to spell in the third. The fact is that if the word “thirdly” will stand as an adverb in a sentence, you must write it with a hyphen. All such adverbs: first, second, third, etc., are written with a hyphen. For example: "Thirdly, you need to mention an adverb." Here the “third” is the adverb, as well as the introductory word, which must be separated by a comma.
There are also cases where the word is spelled separately. If this word fulfills the role of a numeral in a sentence, it must be written separately with “in”. For example: "In the third rows." Here the "third" is the ordinal number. It is easy to define it: in what ranks? - in the ranks of the third. If there is a word from which you can ask a question for a numeral, then we are dealing with an ordinal numeral, which we write separately with the preposition "in".
Conclusion: this word can be written separately or hyphenated.