Taken from the book "Things Not Generally Known" by John Timbs, David Ames Wells. ©1857
The title of Filibusters is a mere corruption of the English word freebooters—a German term imported into England during the Low-Country wars of Elizabeth's reign. It has been erroneously traced to the Dutch word/r/JoaJ; but the Jesuit traveller Charlevoix asserts that, in fact, this species of craft derived its title from being first used by the Flibustiers, and not from its swiftness. This, however, is evidently a mistake, as Drayton and Hakluyt use the word; and it seems to bo of even earlier standing in the French language. The derivation from the English word freebooter is at once seen when the * in Flibustier becomes lost in pronunciation.—C. W. Thorribury.
The term was revised in the mid 19th century to describe the actions of adventurers who tried to take control of various Caribbean, Mexican and Central-American terrorists. (According to Wikipedia)
The first well known political filibuster was U.S. Senator Henry Clay with regard to a bank bill he was in favor of. This filibuster took a month in 1841 and ended on March 11th.
Filibusters continued in the Senate's history during the rest of the 19th century by the end of the century the term was in common usage.