adverb
In twain is an adverbial phrase that means into two parts or pieces.
preposition
In twain is a prepositional phrase that indicates a division or separation into two parts.
-
The sword sliced the fabric in twain with one swift motion.
-
I accidentally ripped my pants in twain while trying to do a split.
-
I tore that piece of paper in twain because I was so frustrated.
-
The betrayal tore their friendship in twain, leaving them estranged.