The word "unaffected" here is closer to the word "sincere." "Piety" should be read as "faith." In this sentence, Goldsmith means that wittiness and religious faith can be found in the same person.
The phrase "Allons!" is French for "Let's go!" Well-educated members of the landed gentry, especially women, were expected to be at least conversant in French.
The phrase "tete-a-tete" is French for "head-to-head," which describes a very intimate conversation between two people who are talking quietly with their heads touching or very close.
Note that Hardcastle says "reserved," which means modest. Kate changes that to "sheepish," a word that describes an overly modest (withdrawn) person who has no self-confidence.
"set my cap to some newer fashion..."See in text(Act The First)
The phrase "set my cap" often means to settle one's attention on another, better, marriage prospect. In other words, Kate will look for another marriageable man.
"Little Aminadab" is the biblical name of a Hebrew prophet and would be most likely used for a person of color or a Jew, in this case, a child of perhaps 10 years old.
In other words, Constance Neville is all show; her beauty is the result of artificial things that might be stored in a bandbox, a cardboard box that is used to hold articles of clothing.
"Miss Rickets of Crooked Lane..."See in text(Act The Second)
A clever play on words—Goldsmith plays on the word Rickets, which would have reminded the audience of Rickets, a disease caused by the lack of Vitamin C, that causes arms and legs to become deformed (Crooked Lane).
" I never nicked seven that I did not throw ames ace three times following..."See in text(Act The Third)
Marlow uses gambling terms to describe his bad luck at seducing Miss Hardcastle. In other words, for every time Marlow has thrown a seven (a winning number), he has thrown three sets of ones, usually a losing number.
"Lady Betty Blackleg, the Countess of Sligo..."See in text(Act The Third)
"Blackleg" is slang for a card shark, and the fact that she's from a relatively poor area of Ireland, an already poor country, indicates her title is probably false.
"the bounce of a cracker..."See in text(Act The Third)
A cracker is a toy used during celebrations. It's a foil-wrapped paper cylinder with a small cap inside that explodes when the two ends of the cylinder wrappers are pulled, creating a cracking sound. Usually, there are several small, cheap toys inside the cylinder.
This refers to St. Mary of Bethlehem Royal Hospital in London, which took care of the mentally ill and from which we get the modern word bedlam, meaning utter chaos.
"The DULLISSIMO MACCARONI..."See in text(Act The Fourth)
Dullissimo is a made-up Italian-sounding word meaning really stupid, and Maccaroni, a real Italian word, was used for young Englishmen who traveled to the Continent and came back wearing Italian fashions and imitating Continental behavior.
