Hot dog. The OED cites the first usage in 1892: "The ‘hot dog’ was quickly inserted in a gash in a roll, a dash of mustard also splashed on to the ‘dog’ with a piece of flat whittled stick, and the order was fulfilled." Etymonline.com says the name "is said to echo a 19th century suspicion (occasionally justified) that sausages contained dog meat."
Liberty. That one's easy—comes from the Latin liber, or "free." It is, of course, related to "liberal," which has been deployed as praise and as pejorative over the centuries, but first appeared in the mid-14th century to mean "selfless" and "noble" and "abundant."
As Ambrose Bierce wrote in his Devil's Dictionary: "Conservative, n. A statesman who is enamored of existing evils, as distinguished from the Liberal, who wishes to replace them with others."
The OED cites the first usage as a 1384 translation from 2 Corinthians: "Forsooth where is the spirit of God, there is liberte."
Fireworks. The OED points to the first usages, in the first years of the 1600s, as broad: military, pyrotechnic, and even "tobacco smoking." But Etymonline.org says about "fire": "PIE [Proto-Indo-European, the common ancestor to languages as diverse as Celtic, English, Sanskrit, and Kurdish] apparently had two roots for fire: *paewr- and *egni- (cf. L. ignis). The former was 'inanimate,' referring to fire as a substance, and the latter was 'animate,' referring to it as a living force." Fire is alive!
America. You know this story—the navigator Amerigo Vespucci and all that. But where did "Amerigo" come from? Etymonline.com says: "The name Amerigo is Germanic, said to derive from Goth. Amalrich, lit. 'work-ruler.'" The origins of our national name are surprisingly boring. (Or, for the Marxists in the house, unsurprisingly labor-oriented.)
Freedom. Our liberty comes from Latin, but our freedom comes from the Old English freodom, which comes from the Proto-Indo-European prijos, meaning "dear" or "beloved."
Etymonline.com says of prijos: "The primary sense seems to have been 'beloved, friend, to love'; which in some languages (notably German and Celtic) developed also a sense of 'free,' perhaps from the terms 'beloved' or 'friend' being applied to the free members of one's clan, as opposed to slaves..."
And a note on freedom from the old storyteller Utah Philips (while he was talking about the IWW's Spokane free-speech fight of 1909):
The state can't give you free speech, and the state can't take it away. You're born with it, like your eyes, like your ears. Freedom is something you assume, then you wait for someone to try to take it away. The degree to which you resist is the degree to which you are free...
Happy freedom, everyone.