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.
There are also some contexts in which x was chosen specifically to indicate something unknown or extra, such as when the German physicist accidentally discovered X-rays in 1895 while experimenting with cathode rays and glass.
Source: https://phys.org/news/2023-08-unknown-algebra-math-mystery.html