During a filibuster, a senator or group of senators continue to talk, often about irrelevant topics (reading the telephone book is a phrase often used), in order to prevent a vote on a particular subject. The rules of the US Senate allow for unlimited debate. So as long as the vocal cords of the senators hold out, they can prevent legislation from moving forward. The term is technically not restricted to the US Senate, but given the peculiar rules of this body it is most often used in reference to that body.
A filibuster is so-called because the minority hijacks the debate, much like a pirate hijacks a ship and it is an affront to good order and discipline, just like the Yankee filibusters who invaded Latin America in the 1850s.
This American political term derives from the Dutch vrijbuiter, or free-booter, a term applied to pirates in the Caribbean in the 16th century. From William Garrard’s The Art of Warre, written sometime before 1587:
Such...as bring wares to the campe, he must take order that they be courteously...vsed...procuring them a conuoy...to the intent they may...remaine...satisfied, without suspect of being robbed...of theeues and flibutors.
And from the same source:
Clearing...the hye wayes...from fleebooters.
Later uses of filibuster are borrowings from the French flibustier and influenced by the Spanish filibustero, the latter especially in regards the following sense of the word.
In the 1850s, various expeditions were organized in the U.S. to foment revolution in Latin America. These were called filibusters and the movement as a whole was known as filibusterism because such actions were considered piratical under international law. From James Russell Lowell’s 1854 Cambridge Thirty Years Ago:
He who was ordained to-day might...accept a colonelcy of filibusters to-morrow.
The modern legislative sense is claimed to date to the slavery debates of the 1850s, but it is not attested to until well after the Civil War. From the NY Times, 3 May 1876:
BUSINESS IN THE SENATE
THE APPORTIONMENT BILL—DEMOCRATIC FILIBUSTERING—REPUBLICANS WHO VOTED WITH THEM [...]
ALBANY, Tuesday, May, 2, 1876
When the Apportionment bill came up for its third reading to-day the Democrats, not with the hope of preventing its passage, but for the purpose of defeating a number of reform measures now pending, commenced to filibuster.
It’s interesting to note that this is not only the earliest reference to legislative filibustering of which I’m aware, but it is in reference to a state legislature, not the US Senate. For an early federal reference there is this from the Congressional Record of 11 February 1890:
A filibuster was indulged in which lasted...for nine continuous calendar days.
(Source: Oxford English Dictionary, 2nd Edition; Proquest Historical Newspapers)
Copyright 1997-2014, by David Wilton