Two of a kind (like Mark?) (5)

I believe the answer is:

twain

(Other definitions for twain that I've seen before include "Mark ___ , American writer" , "Mark -, Huckleberry Finn author" , "Mark, US writer" , "Mark . . . . . was the pen name of Samuel Langhorne Clemens" , "Kipling denied ever meeting" .)

I've seen this clue in The Guardian.

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