Which Is Correct Second or Secondly?

And “secondly” is an adverbial form that makes no sense at all in enumeration (neither does “firstly”). As you go through your list, say simply “second,” “third,” “fourth,” etc.

Is it second or secondly?

The trouble is, secondly is not the proper word. It's just plain old second, with no ly ending. Dave Dowling explains it like this in The Wrong Word Dictionary: “First, an adverb, does not need an ly.”¹ The ly on secondly is superfluous, unnecessarily taking up precious talk time.

Is it first and second or secondly?

You should use first, second, and third to show textual enumerations in your writing. Many authorities prefer first, not firstly, even when the remaining items or points are introduced with secondly and thirdly. Example: First, through practice you will develop a better style.