Killer
Part of speech: adjective
Definition: Excellent, very good.
Part of speech: noun
Definition: That which kills. That which causes stress or is extremely difficult, especially that which may cause failure at a task. Something that is so far ahead of its competition that it effectively kills off that competition. A diacritic mark used in Indic scripts to suppress an inherent vowel (e.g., the Hindi viram, the Bengali or Oriya hasanta) or render the entire syllable silent (e.g., the Burmese virama, the Khmer toandakhiat).
Example sentence: It is the hopeful, buoyant, cheerful attitude of mind that wins. Optimism is a success builder; pessimism an achievement killer.
Slayer
Part of speech: noun
Definition: One who slays; a killer; a murderer; a destroyer of life.