Appendix:English ordinal numbers
English has several series of ordinal numbers, representing position in a sequence: a main series of commonly used adjectives, beginning first, second, third; a series of Latinate adjectives, beginning primary, secondary; and a series of Greek prefixes, beginning proto-, deutero-.
The main series is formed regularly from lower cardinal numbers, starting with the single digits, by replacing the last word with the corresponding ordinal (e.g., “twenty-first”, “hundred-twentieth”), or suffixing -th to a single word (e.g., tenth), or -eth for the multiples of ten ending in -y (e.g., twentieth). The Latinate series is formed from Latin numbers, but numbers above tertiary are very rare, and frequently confused with arities, which also end in -ary but are based on Latin distributive numbers, not ordinal numbers. The Greek series is quite technical, and obscure beyond deutero-, which is itself uncommon.