tcsh is a Unix shell, based on (and compatible with) the C shell. It is essentially the C shell with filename completion, command-line editing, and a few other features. The 't' in tcsh comes from the T in TENEX[?], an operating system which inspired the author of tcsh.
... discovered Hudson Bay
Alexander von Humboldt, (1769-1859), explored Central and South America, visited Siberia
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Helge Ingstad, (1899-2001), Norwegian, Danish ...