There are a few words that appear in most Regency romances that are uncommon in other cotemporary writing.
They are far from the only differences between modern speech and Regency speech, but they are used to give a flavor.
"Ton" means fashionable society.
"Cozen" means to trick or deceive.
"Chit" is an impudent or arrogant young woman. In RR usage, it implies youth or immaturity.
A "night rail" was a robe or dressing gown. The OED definition surely implies wear outside of bed. RR usage seems fo me to be wear in bed.
A "Blue Stocking" is a gentlewoman with literary or intellectual aspirations.