One who or that which kills. / (figuratively) That which causes stress or is extremely difficult, especially that which may cause failure at a task.

(slang) Excellent, very good, cool. / Causing death, destruction, or obliteration. / Distressing, uncomfortable.

plural of killer

plural of killer whale

A technological product that is so good, or so innovative, that it is irresistible to potential customers; especially a software product that persuades people to buy the hardware needed to use it.

A person who commits multiple (more than two) murders, especially similar ones with no obvious motive over a period of time with a "cooling-off" period between each murder.

Someone or something, especially a sports team, that defeats a larger and superior opponent.

(business, US) A retailer that offers a wider selection of merchandise in a category than existing retailers, at lower prices, thereby gaining substantial share of the market and "killing" the existing retailers.

plural of killer app

plural of killer poke