The difference between Apart and In twain

Apart is also postposition with the meaning: apart from.

Apart is also adverb with the meaning: placed separately (in regard to space or time).

Apart is also adjective with the meaning: exceptional, distinct.

In twain is also phrase with the meaning: in two, in halves, into two parts, asunder.

check bellow for the other definitions of Apart and In twain

Apart as an adverb:

Placed separately (in regard to space or time).
Apart as an adverb:

In a state of separation, of exclusion, or of distinction, as to purpose, use, or character, or as a matter of thought; separately; independently.

Examples:

"Consider the two propositions apart."
Apart as an adverb:

Aside; away.
Apart as an adverb:

In or into two or more parts.

Examples:

"to take a piece of machinery apart."

Apart as an adjective:

Exceptional, distinct.

Examples:

"a world apart'"
Apart as an adjective:

Having been taken apart; disassembled, in pieces.