Crossword Dictionary

Slay

slay, slain, slays, slayed, slaying, slayable - v 
to kill violently 

slain - a 
killed; `slain' is formal or literary as in "slain warriors"; "a picture of St. George and the slain dragon" 

wordplays

synonyms

carried off, claimed, croaked [slang], destroyed, dispatched, done in, felled, killed, taken, bumped off, butchered, cut down, finished, got (or gotten), iced [slang], knocked off, murdered, neutralized, offed [slang], put away, rubbed out, scragged, snuffed, taken out, wasted, whacked [slang]

in a sentence

millions have been slain worldwide by this dreadful disease

vowed to slay without mercy whoever was responsible for murdering his family

It's a lot easier to slay a vampire with a stake in the heart than it is to slaysome of our demons that are in our heads."

merriam-webster

etymology 

Middle English slÄ“n, from Old English slean "to smite, strike, beat," also "to kill with a weapon, slaughter" (class VI strong verb; past tense sloh, slog, past participle slagen), from Proto-Germanic *slahanan "to hit" (source also of Old Norse and Old Frisian sla, Danish slaa, Middle Dutch slaen, Dutch slaan, Old High German slahan, German schlagen, Gothic slahan "to strike"). The Germanic words are said to be from PIE root *slak- "to strike" (source also of Middle Irish past participle slactha "struck," slacc "sword"), but, given certain phonetic difficulties and that the only cognates are Celtic, Boutkan says the evidences "point to a North European substratum word."

etymonline