Now it's not possible to ensure every single word is correct unless you want to research the etymology of your entire book and some words we simply can't trace, but this is a sort of guide to what should and should not be in Regency and Victorian books. I intended to write out a reference list mostly for myself but I had done some searching myself for reference lists to save the tiresome double-checking and hadn't found any so I thought it might be nice to share. It's a rather odd collection of words but I hope someone finds it useful and maybe interesting.
Now all of my medieval works are set before we moved to Old English so I don't worry so much about my language in those books but obviously I don't include modern concepts. Though I don't use it as it's strange for a Brit like me the word gotten--which fell out of use here in Regency times--is an Old English word.
Some of these are ones my friends have pointed out that drive them mad:
Stoop - This is an Americanism and we would say doorstep.
Sidewalk - Brits say pavement.
Drive or driveway (as in road leading to a house) - This didn't come into use until very late in the Victorian era. The safest phrase is private road.
Climax - As in orgasm. The other use also didn't come into use until early 1800's so it's no good at all for Regency set books. It wasn't used until 1880 for describe a sexual orgasm.
Table-manners - This comes in at the start of the Victorian period.
Hypnotic (i.e. His hypnotic gaze) - This came into use around 1843. Previously it meant 'inducing sleep.'
Unconscious - During the Regency era and into the Victorian era this meant 'not conscious' of something rather than being knocked out. I often say knocked senseless in Victorian and Medieval works. Like-wise self-conscious didn't change it's meaning until mid-Victorian era. Before that it meant simply being aware of what you are doing but only came into use at all after the Elizabethan era.
Vantage meaning vantage point came into use after 1865.
Needlepoint - As in lacework. No sitting doing needlework for our heroines until after 1865.
Lanky - This didn't come in until around 1818 and even then it appears to have been a slang word and likely not used by upper classes.
Phew, There are more.But this are ones I see quite often. It's hard to be entirely accurate and some say they don't mind the use of more modern words in narration as long as it's not coming out of character's mouths, but I do think an admirable attempt at accuracy is always nice. And I'll admit it, I'm a word geek. I love finding the history of words and seeing how my ancestors used them. I hope someone finds this interesting or useful :)