Merriam-Webster

A widow holding property or a title from her deceased husband : a dignified elderly woman.

Wiktionary

Any lady of dignified bearing.
(Also had the same definition as M-W above)

Additional info

Dowagers in romance novels are often depicted as formidable women, either as the widowed mother or aunt of the hero or a particularly powerful woman in society. A reader may also run into the term “dower house.” Wikipedia defines this as, “A dower house is usually a moderately large house on an estate which is occupied by the widow of the late owner. The widow, often known as the “dowager” usually moves into the dower house, from the larger family house, on the death of her husband, the new heir occupies the now vacated principal house.”

This is a term used for a debutante that is the cream of the crop — beautiful, poised and perfect.

Merriam-Webster

A young woman making her formal entrance into society.

The debutante in romance novels will be around 18 years of age. This age can vary, for many reasons — death in the family, readiness, female politics, etc. A debutante has her “come out” where she is introduced to society.

Merriam-Webster

A pert young woman.

1811 Vulgar Tongue

An infant or baby.

Wiktionary

A child or babe; as, a forward chit; also, a young, small, or insignificant person or animal.

Example

“Did you meet the Martindale chit?”
“Who?”
“The girl barely out of the schoolroom who is drowning in white ruffles over there.”

A bawd, the mistress of a brothel.

–From the 1811 Dictionary of the Vulgar Tongue.

May also be referred to as lady abbess — if you’re feeling gentlemanly.

An old maid; their punishment after death, for neglecting increase and multiply, will be, it is said, leading apes in hell.

–From the 1811 Dictionary of the Vulgar Tongue.

This one occasionally pops up in Regency novels. Awful, isn’t it?