I read in a book:
四声(sì​shēng) which is translated in the book as "the four tones"
Somewhere else in the same book, I read:
三声变调(sānshēngbiàn​diào) which is translated as "The third tone sandhi"

In the first example, (number+noun) is translated as a cardinal number.
But in the second example, (number+noun) is translated as an ordinal number.
It's just confusing.
How should one say "The fourth tone"? and make it different from "the four tones"?