1: an irregular military adventurer; specifically : an American engaged in fomenting insurrections in Latin America in the mid-19th century
2 a : the use of extreme dilatory (see dilatory 1) tactics (as by making long speeches) in an attempt to delay or prevent action especially in a legislative assembly
b : an instance of this practice
The filibuster delayed the voting on the bill for over a week.
They engaged in a filibuster that lasted for over a week.
More details, and notable examples of filibuster, can be found in this Wikipedia article: Filibuster in the United States Senate
Spanish filibustero, literally, freebooter
First Known Use: 1851