Slaughter, n.
Etymology: [OE. slautir, slaughter, slaghter, Icel. slatr slain flesh, modified by OE. slaught, slaht, slaughter, fr. AS. sleaht a stroke, blow; both from the root of E. slay. See Slay, v. t., and cf. Onslaught.]
The act of killing. Specifically: (a) The extensive, violent, bloody, or wanton destruction of life; carnage. On war and mutual slaughter bent. Milton.
(b) The act of killing cattle or other beasts for market.
Syn. -- Carnage; massacre; butchery; murder; havoc.
1 other Webster entry under this spelling
Slaughter, v. t. [imp. & p. p. Slaughtered; p. pr. & vb. n. Slaughtering.]
1. To visit with great destruction of life; to kill; to slay in battle. Your castle is surprised; your wife and babes Savagely slaughtered. Shak.
2. To butcher; to kill for the market, as beasts.
Shades of meaning
Fernald has no entry of its own for slaughter; he lists it under kill, massacre.
Where he writes about it:
Butcher and slaughter apply primarily to the killing of cattle; massacre is applied primarily and almost exclusively to human beings, signifying to kill them indiscriminately in large numbers; to massacre is said when there is no chance of successful resistance; to butcher when the killing is especially brutal; soldiers mown down in a hopeless charge are said to be slaughtered when no brutality on the enemy's part is implied. — from kill
Carnage (Latin caro, carnis, flesh) refers to widely scattered or heaped up corpses of the slain; slaughter is similar in meaning, but refers more to the process, as carnage does to the result; these two words only of the group may be used of great destruction of life in open and honorable battle, as when we say the enemy was repulsed with great slaughter, or the carnage was terrible. — from massacre