I've already written a post about the slang used in the Regency Era. But it is impossible to cover such a broad topic in one post, so here are 15 more words and expressions that were common at the time, but can now only be found in some old books:
Books: cards to play with. If someone placed the cards in the pack in an unfair manner, then they'd be "planting the books".
Cap Acquaintance: people who barely knew each other, only enough to salute with the hat or bow when they met.
Execution Day: washing day.
Family Man: a thief, or receiver of stolen goods.
Gentleman Of Three Outs: someone without money, wit and manners.
Kings' Pictures: coins
Master Of The Wardrobe: someone who pawns his clothes to buy liquor.
Mushroom: a person or family of humble origin who has suddenly become wealthy and influential.
On Saint Geoffrey’s Day: never (there was no St Geoffrey's Day).
Scandal Broth: tea.
Squash: a party you don't want to attend but must anyway.
Toad eater: an impoverished gentleman or female relation that was hired as a paid companion.