“The roots of ‘filibuster’ go back to a Dutch word for a pirate or privateer, ‘vrijbuiter.’ …. Dutch colonists of the 16th century used the term for pirates they encountered in the West Indies. In English it became ‘freebooter,’ in French ‘flibustier’ and in Spanish ‘filibustero.’
“In the mid-19th century, ‘filibustero’ became a key term in Latin America as soldiers of fortune, often hailing from the U.S., went on unauthorized expeditions to overturn Spanish colonial rule and take control of territories for themselves. These adventurers earned the ‘filibustero’ label, Anglicized as ‘filibuster’ in the American press….
“[In 1853] the word came up as the House of Representatives debated whether to annex Cuba. A North Carolina Democrat, Rep. Abraham Venable, broke with his party to denounce the idea as U.S. piracy, or as he put it , ‘now in our tongue filibuster, but still a freebooter.’ His fellow Democrat, Rep. Albert G. Brown of Mississippi, turned the label around on him — and began its transition to a new political meaning about hijacking the debate itself. ‘When I saw my friend standing on the other side of the House filibustering, as I thought, against the United States, surrounded, as he was, by admiring Whigs, I did not know what to think.’ ”
— From ” ‘Filibuster’: A Pirating Maneuver That Sailed Into the Senate” by Ben Zimmer in the Wall Street Journal (Sept. 25, 2020)