Synonyms that are in the dictionary are marked in green. Synonyms that are not in the dictionary are marked in red.
Antonyms that are in the dictionary are marked in green. Antonyms that are not in the dictionary are marked in red.
However, a lot of them have dual-typing and there are only 12 pure Steel-type Pokemon in the franchise, including a new one introduced in Pokemon Scarlet & Violet.
Source: https://gamerant.com/pokemon-every-pure-steel-type-pokemon-ranked/