slay / slew / slain / slayed
The past forms of slay.
For kill, the past is slew and the past participle is slain, after forms of have and forms of be: The knight slew the dragon. The dragon was slain. Slayed is informal for impressed in talk about performances. Do not use slayed for a killing.
Examples
UseThe hunter slew the wolf.
UseThe wolf was slain.
AvoidThe hunter slayed the wolf.