Vorpal sword is a phrase used by Lewis Carroll in his nonsense poem "Jabberwocky".
Carroll published Through the Looking-Glass in 1871. Near the beginning, Alice discovers and reads "Jabberwocky". The word "vorpal" appears twice in the poem, which describes a young boy's quest to slay a monster called the Jabberwock:
And later,
As with much of the rest of the poem's vocabulary, the reader is left to guess at the meaning of "vorpal" from the context. It is commonly assumed to mean "deadly" or "sharp", but could also be referring to the material of which the sword is composed. Some readers have imagined other properties the word could describe. Alexander L. Taylor points out in his Carroll biography The White Knight that "vorpal" can be formed by taking letters alternately from "verbal" and "gospel".[1]
Carroll himself once wrote, "I am afraid I can't explain 'vorpal blade' for you—nor yet 'tulgey wood.'"[1]
In the game Dungeons & Dragons, a Vorpal Sword is defined as a sword with the magical effect that it tends to cut off opponents' heads. This makes sense in that the poem's plot results in the hero carrying away the head of the Jabberwock.