Generally speaking, history tells us that pirates and their ilk had nasty tempers. I have not only imaginings but a fair amount of historical evidence that tells me certain gentlemen in the trade (and perhaps the ladies too) would go off half cocked when called an out and out pirate. Particularly in public. Henry Morgan shot men for it. Francois L'Olonais cut tongues out over it. And I like to imagine Anne Bonny refusing her favors to guys that used her name and the term in the same sentence.
The words that apply to the trade get mixed up and interchanged, like a bad tossed salad. Triple P is here, if for no other reason, to set the record straight. (Plus I'm sick as a dog and not quite prepared to be particularly eloquent.) So here's a handy list for your perusal.
Pirate: a sea-robber. Comparable to the old term applied to land robbers: highwayman. There is no commission legitimizing the taking of prizes in the case of a pirate. Pirate may refer to the individual or the ship pursuing such activity. It must be noted, I think, that many so called privateers slipped into the realm of pirate at one point or another in their careers.
Privateer: a private ship fitted out by its owner to cruise against and enemy. The captain is granted sanction to do so by his government via a letter of marque which may be revoked if its parameters are violated (i.e., if the ship takes prizes from countries other than the one named). Privateer, again, may refer to the ship or the man. The key here is the letter of marque and the fact that a prize is not legitimate until it is libelled in court, with a tenth of the booty going to the admiralty or the government.
Corsair: the English word for a French privateer - corsaire.
Buccaneer: originally, this word had nothing to do with sea roving. It came from the French word boucanier. Many former French indentured servants migrated to the Island of Hispanola in the mid-17th century where they earned their keep by hunting the wild game on the island. The local Arawak natives taught the men how to smoke the meat to preserve it. A boucan was the traditional smokehouse used for the purpose. When the Frenchmen, along with some Dutch and English folks as well, went to sea the word followed them and was Anglicized as buccaneer. They were, for the most part, pirates with a particular hatred for their former Spanish overlords that led them to raid not only shipping but towns along the Spanish Main as well.
Freebooter: another English term for the French buccaneer or corsair which originally had a particular contemptuous connotation.
Filibuster: started out as another term for buccaneer and morphed in meaning during the various wars for Central and South American independence. A filibuster became any seaman or soldier of fortune who engaged in warfare, against a state that his country of origin was not at war with, for financial gain. It was further convoluted in the 19th century to referred to not only individual mercenaries but groups of speculators who supplied arms to new countries like Mexico and Texas in exchange for cash. From there, it started clogging up Congress and does to this day.
Sea dog: the Elizabethan privateers such as Drake and Hawkins.
Sea rovers: generally pirates but sometimes applied to privateers as well.
Sea wolves: almost exclusively privateers.
Swashbuckler: this word is not a literary invention but its application to the trade is. In the 16th century a swashbuckler was a highwayman or bandit who lay in wait for unsuspecting travelers and robbed them on the road. In the late 18th and early 19th century, Romantic novelists began using the term to refer to sea robbers upon whom they were casting an ambiguously titillating light. There are novels from the mid-1800s that frequently refer to Edward Teach and Jean Laffite as swashbucklers. And the ladies swooned.
Learn 'em, know 'em, live 'em, Brethren, and spice up your language appropriately. Just be careful who you call a "pirate". Or learn the hard way.