What do we call the “rd” in “3ʳᵈ” and the “th” in “9ᵗʰ”? The addition of -th -eth relates to numbers 4 to 20 (and similarly,) and is a suffix to the cardinal number However, as in the second and third examples, the rd st simply come from the right-end of the word for the ordinal number:
etymology - What is the origin of the -th suffix? What is the . . . 2 th as suffix changes the verb or adjective to a noun - no dispute there What does making it a noun add to the meaning? It often seems to mean a state of: eg Strength - a state of strong Health as a state of healing, Width as a state of wide, etc