killer

1. One who or that which kills.

   Carbon monoxide is a silent killer.

2. That which causes stress or is extremely difficult, especially that which may cause failure at a task.

   That test was a killer.

3. Something that is so far ahead of its competition that it effectively kills off that competition.

   Digital streaming platforms are CD killers.

4. A knockout form of darts or pool involving several players.
5. A club used for killing fish.
6. A particularly heavy type of handstamp, or portion of one, often obscuring a large part of the postage stamp.
7. A diacritical 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).

1. Excellent, very good, cool.

   killer feature

2. Causing death, destruction, or obliteration.

   killer bee

3. Distressing, uncomfortable.

   I had a killer headache this morning.

noun

A sea mammal related to dolphins and porpoises (Orcinus orca).