filibuster (n.)
1580s, flibutor "pirate," probably ultimately from Dutch vrijbuiter "freebooter," used of pirates in the West Indies as Spanish filibustero and French flibustier, either or both of which gave the word to American English (see freebooter).
Used 1850s and '60s of lawless adventurers from the U.S. who tried to overthrow Central American countries. The legislative sense is first recorded c.1851, probably because obstructionist legislators "pirated" debate. Not technically restricted to U.S. Senate, but that's where the strategy works best. The verb is recorded by 1853 in both the freebooting and the legislative senses.
From: www.etymonline.com [emphasis added]
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