re: Why is "Martian" spelled with a "t"?

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In Latin, the nominative declensions of nouns tend to be truncated forms of the full roots—that’s why Latin nouns are often listed by their genitive declensions instead. In the case of Mars, the genitive is “Martis”—so derived forms usually include the “t”. (That’s also where we get the martial in “martial arts”.)

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