The Collaborative International Dictionary of English v.0.48:

Slay \Slay\, v. t. [imp. Slew; p. p. Slain; p. pr. & vb. n.
   Slaying.] [OE. slan, sl?n, sleen, slee, AS. sle['a]n to
   strike, beat, slay; akin to OFries. sl[=a], D. slaan, OS. &
   OHG. slahan, G. schlagen, Icel. sl[=a], Dan. slaae, Sw. sl?,
   Goth. slahan; perhaps akin to L. lacerare to tear to pieces,
   Gr. ????, E. lacerate. Cf. Slaughter, Sledge a hammer,
   Sley.]
   To put to death with a weapon, or by violence; hence, to
   kill; to put an end to; to destroy.
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         With this sword then will I slay you both. --Chaucer.
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         I will slay the last of them with the sword. --Amos ix.
                                                  1.
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         I'll slay more gazers than the basilisk. --Shak.
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   Syn: To kill; murder; slaughter; butcher.
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WordNet (r) 3.0 (2006):

slaying
    n 1: unlawful premeditated killing of a human being by a human
         being [syn: murder, slaying, execution]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "slaying":
   bane, blood, bloodletting, bloodshed, braining, dealing death,
   destruction, destruction of life, dispatch, euthanasia, execution,
   extermination, flow of blood, gore, immolation, kill, killing,
   lapidation, martyrdom, martyrization, mercy killing, poisoning,
   ritual killing, ritual murder, sacrifice, shooting, slaughter,
   stoning, taking of life