<p><strong>Noun:</strong></p><ul><li>a person or thing that kills.</li><li>killer whale.</li><li>a device used by a post office for printing cancellations on postage stamps.</li><li>a mark of cancellation made on a postage stamp.</li><li>Slang: something or someone having a formidable impact, devastating effect, etc.: The math test was a real killer.</li></ul><p><strong>Adjective:</strong></p><ul><li>Slang: severe; powerful: a killer cold.</li><li>very difficult or demanding: a killer chess tournament.</li><li>highly effective; superior: a killer recipe for fried chicken.</li></ul>