Bogart – This one is not very old, seeing as it originated in 1969. It meant "to hold a joint in your mouth" and leave it dangling from your lip like Humphrey Bogart instead of passing it on. The verb was first used in the movie "Easy Rider". The word was also used in the 1960s, meaning "to get something by intimidation, to be a tough guy". When I was in grades eleven and twelve, my friends and I sometimes referred to cigarettes as "bogarts", so this is one I have quite a fondness for.
Eighty-six – I have such a fondness for some older slang. This word originated around 1936 lunch counters and meant "eliminate". It was a cook's word for "none" when he was asked for something that was unavailable and was likely a rhyming slang for nix. I always feel like this word should be said between barely moving lips with a twist of Mickey Spillane, hat cocked forward to obscure your face in the moonlight.
Finagle – My mother uses this word, and I think she is one of the few people I have heard utter it in regular conversation. It means “to obtain by indirect or involved means; to obtain by trickery” or “to use devious or dishonest methods to achieve one’s ends”. No one knows where this word comes from. It is likely a mispronunciation of a word found in several English dialects. For instance, fainaigue means “to misplay a card; to play a card of the wrong suit” in Newfoundland, Canada, but this word is of unknown origin as well.
Gambol – This one still shows up in poetry, but that's where words often go to die. It means "to skip about in play". This verb first showed up in 1508. The Greek kampe meant "bend", then the Late Latin gamba meant "horse's hock or leg". From there, the Middle French gambada moved to the 1513 word gambolde, meaning "a leap or spring".
Gnash – Maybe we use this one less because there is less fear of Hell these days. It means "to strike or grind (as the teeth) together". It possibly originated with the Old Norse gnastan, meaning "a gnashing", and it may have been imitative. It shows up around 1300 in Middle English as gnasten, which meant "to gnash the teeth", and then as its modern variant in 1496.
Jape – This is a word I use in Scrabble to piss people off. It means "to say or do something jokingly or mockingly" or "to make mocking fun of". It first showed up around 1300 as "to trick or beguile", possibly from the Old French japer, which meant "to howl", or from the Old French gaber, which meant "to mock, deride". It took on the slang sense of "to have sex with" around 1450, and then disappeared from polite language. It found its second wind in Middle English with the meaning "to say or do something in jest".
Moil – I've always liked the sound of this word, because it sounds like a much muckier and slogging version of the word "toil". It turns out that it means exactly that: "to labour in the mire". It came about around 1400, possibly from the Old French mouiller meaning "to wet, moisten", which may in turn be related to the Vulgar Latin molliare and the Latin molis, meaning "soft".
Plash – This word is so close in meaning to another very like it that it could be considered almost useless, but not by me. There is a feeling to this word that the other doesn't have. Sadly, this, too, has been relegated almost solely to poetic works. It means "to cause a splashing or a spattering effect" or "to break the surface of (water)". It was first recorded in 1513 as meaning "noise made by splashing", derived from the Old English plæsc, which meant "pool of water, puddle".
Roil – This is a natural one to include, because my insides are doing it. It means "to make turbid by stirring up the sediment or dregs of". It began with the Latin noun robigo meaning "rust", in the Old French rouiller it was "mud, rust", in the Middle French rouil it became the adjective "muddy, rusty", and in the Middle English roil it became a verb meaning "to roam or rove about". It has been about in its present form since 1590.
Whelm – We are often overwhelmed, I have even experienced being underwhelmed, but there is not a whole lot of whelming going on these days. I can't even recall the last time I whelmed. Its first definition is "to turn (as a dish or vessel) upside down usually to cover something; to cover or engulf completely usually with disastrous effect", and the second definition is "to overcome in thought or feeling". There is no first date of appearance, but it showed up in Wessex Saxon as hwielfan, in Mercian as hwelfan and ahwelfan, which meant "cover over" and was probably altered by association with the Old English helmian, "to cover".