"A half a Vorpal's special, please."
Illustration to the poem Jabberwocky 1871
Public DomainIllustration to the poem Jabberwocky 1871 - Credit: Sir John Tenniel (1820-1914).

Vorpal sword is a phrase coined by Lewis Carroll in the nonsense poem Jabberwocky. The poem is contained in Through the Looking Glass (1871), which continues the adventures of Alice in Wonderland. 

The word "vorpal" appears twice in "Jabberwocky," a poem describing a young boy's quest to slay a monster called the Jabberwock.  The boy “took his vorpal sword in hand”“The vorpal blade went snicker-snack!

Readers and scholars have speculated about exactly what vorpal means.  It probably had very little meaning when Carroll composed the poem, which consists almost entirely of nonsense words.  Indeed, Carroll himself once wrote, "I am afraid I can't explain 'vorpal blade' for you—nor yet 'tulgey wood.'" 

However, the word has since entered the English language, and has thus been assigned various definitions.  In current usage, it is sometimes used to refer to an extremely effective weapon capable of severing a head or a limb with a single blow.