Halcion is the brand name for a central nervous system (CNS) depressant benzodiazepine.The generic name is Triazolam and it has pharmacological properties similar to other benzodiazepines. Halcion is generally used as a sedative to treat severe insomnia. In addition to the hypnotic properties, triazolam possesses amnesic, anxiolytic, sedative, anticonvulsant and muscle relaxant properties. It is limited in use because it has a short half-life as it is not effective for patients that suffer from frequent awakenings or early wakening.

Halcion was patented in 1970 and went on sale in 1982 in the United States.

The other 3 choices concern the word Halcyon as it is a castle, song title and a family of birds (Halcyonidae).

More Info: en.wikipedia.org