Latin word once used in various phrases in English, often in legal language, where it means "the condition of something, the matter in hand or point at issue;" literally "thing" (see re). For example res ipsa loquitur "the thing speaks for itself;" res judicata "a point decided by competent authority."

"servile black man," 1922, somewhat inaccurately in reference to the humble, pious, but strong-willed main character in Harriet Beecher Stowe's novel, "Uncle Tom's Cabin" (1852). The image implied in the insult perhaps is more traceable to the late 19c. minstel show versions of the story, which reached a far wider audience than the book.

I don't recall anyone in the 1920s using the term 'Uncle Tom' as an epithet. But what's amazing is how fast it caught on (in the 1930s). Black scholars picked up (the term) and just started throwing it at each other. [Ernest Allen, quoted in Hamilton, Kendra, "The Strange Career of Uncle Tom," Black Issues in Higher Education, June 2002]

As a verb, attested from 1937.

1794, the name of a fire-protection device to be used in theaters, a literal iron curtain; see iron (n.) + curtain (n.).

The new and exquisitely beautiful theatre of Drury-lane has the peculiar contrivance of an iron-curtain to secure the audience from all danger, in case of fire on the stage. Miss Farren, in the occasional epilogue, delivered on opening this new theatre, pleasantly informs the spectators that, should flames burst out in the part appropriated to the representation, they may comfort themselves with thinking that nothing can be burnt but the scenery and the actors. [The Monthly Review, June 1794]

From 1819 in the figurative sense "impenetrable barrier." In reference to the Soviet occupation of Eastern Europe, famously coined by Winston Churchill March 5, 1946, in speech at Westminster College, Fulton, Missouri, but it had been used earlier in this context (for example by U.S. bureaucrat Allen W. Dulles at a meeting of the Council on Foreign Relations, Dec. 3, 1945). The phrase had been used in the sense of "barrier at the edge of the sphere of influence of the Soviet Union" from 1920. During World War II, Goebbels used it in German (ein eiserner Vorhang) in the same sense. But its popular use in the U.S. dates from Churchill's speech.

"person or thing that people hope will be very successful in the near future," 1911, originally in U.S. sporting use in reference to the quest for a white man capable of beating champion pugilist Jack Johnson.