To kill, murder.
Our foes must all be slain.
To eradicate or stamp out.
You must slay these thoughts.
(by extension) To defeat, overcome (in a competition or contest).
1956, “Giants Slay Bears in Pro Title Battle”, in Lodi News-Sentinel, 1956 December 31, page 8.
To delight or overwhelm, especially with laughter.
Ha ha! You slay me!
To amaze, stun or otherwise incapacitate by awesomeness; to be awesome at something; to kill (slang sense).
To have sex with