Havoc, interj.
Etymology: [See Havoc, n.]
A cry in war as the signal for indiscriminate slaughter. Toone. Do not cry havoc, where you should but hunt With modest warrant. Shak. Cry 'havoc,' and let slip the dogs of war! Shak.
2 other Webster entries under this spelling
Havoc, n.
Wide and general destruction; devastation; waste. As for Saul, he made havoc of the church. Acts viii. 3. Ye gods, what havoc does ambition make Among your works! Addison.
Havoc, v. t.
To devastate; to destroy; to lay waste. To waste and havoc yonder world. Milton.
Shades of meaning
Fernald has no entry of its own for havoc; he lists it under massacre.
Where he writes about it:
Havoc may not be so complete as massacre, nor so coldly brutal as butchery, but is more widely spread and furious; it is destruction let loose, and may be applied to organizations, interests, etc., as well as to human life; "as for Saul, he made havoc of the church," Acts viii, 3. — from massacre