To part in twain; divide; sunder.
"The ancient curse was said to split the mountain in twain, creating a deep chasm between the two villages."
In plain English: To twain is to split something into two separate parts.
"The twin stars twained in the night sky, appearing to merge into a single point of light."
twofold
"The report highlighted a twof increase in both revenue and customer satisfaction after the new policy was implemented."
two
"The twain met in the middle of the river to discuss their plans."
A standard software protocol and applications programming interface (API) that regulates communication between software applications and imaging devices such as scanners and digital cameras.
"Mark Twain was an American author famous for his novels and essays."
A surname.
Twain comes from Old English twēġen, meaning "two," which itself traces back to Proto-Indo-European roots shared by many Germanic languages. Although it survived as an archaic secondary form of two, especially after nouns in Middle English, the word eventually fell out of common use.