numbers - 1st hour, 2nd hour, 3rd hour... But how to say "zero"-th hour?

E.g. in School we have 5-7 or 8 hours every day (Math, History, Biology, Chemistry, English etc.).

The first hour starts at 8:00 A.M.

But every Thursday we have an hour that stars at 7:10 A.M.

In the table it will look like this (just random picture from the web):

In Czech language we call it:

nultá hodina which is something like zero-ish hour

and then 1st, 2nd and 3rd: první, druhá, třetí hodina

How is nultá hodina (the hour that is before the first hour) called in English?

And how do you write it "shortly"? As 0th ? Or somehow else?

Answer

You already had the answer: it’s zeroth.

I think you’ll find that -th is a modestly productive suffix in English for indicating ordinals other than first, second, and third. For example, consider the n^th element in a series, or the i ^th and j ^th indices of (two-dimensional) matrix. You can even find “epsilonth” (ε^th) if you look hard enough.

But that one’s rare; zeroth is not. The OED defines zeroth as:

Coming next in a series before the one conventionally regarded as the first.

Its first citation is from the 19^th century. So the two series work out to be:

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  In words: zeroth, first, second, third, fourth, fifth, . . . three hundred ninety-fifth, . . .

  
  


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  In figures: 0^th, 1^st, 2^nd, 3^rd, 4^th, 5^th, . . . 395^th, . . .