Asunder means into separate pieces, in old use. Torn asunder, put asunder, split asunder.
It survives in two phrases: what God has joined together, let no man put asunder, from the marriage service, and torn asunder, which is deliberately grand. It comes after the verb, never before. Note sunder, the verb it comes from, which is now archaic; and sundry, meaning various, which is the same root about things being separate.
1adverbasunderInto separate pieces, in old use.
“The old wooden ship was torn asunder by the waves and sank.”
asunder is a state of separation.
a-SUNDER → split the way THUNDER splits a tree
The thunder came in the night, and by morning the old tree stood in two pieces.
hooks ontothunder
Middle English asunder is a-, in or on, plus sunder, from Old English sundor, apart. Sundry and the German sondern come from the same separateness.
Proto-Indo-European
*h₂en-
Proto-Germanic
*sundraz — alone, separate
Proto-West Germanic
*sundr
Proto-Indo-European
*h₂en- — on, onto
Old English
onsundrum
Middle English
asunder
English, today
asunder
Built from
From Middle English asunder, asonder (“apart in position, distant; apart in movement; to pieces; alone, separately; distinct in kind, different”), asondri (“distinct, separate”), onsunder, onsondre (“apart, asunder; alone, separately; especially, particularly (?)”), from Old English onsundrum, on sundur (“asunder, apart, privately”), probably from on- (ultimately from Proto-Indo-European h₂en- (“on, onto”)) + sundor, sunder (“alone, apart; separately; privately”) (from Proto-West Germanic sundr, from Proto-Germanic sundraz (“alone, separate”), possibly from Proto-Indo-European senH- (“apart; for oneself; without”)). by surface analysis, a- + sunder. 2
Etymology from Wiktionary, CC BY-SA