The adjective "portentous" refers to one's giving a sign or warning of imminent unpleasantness. It can also refer to someone having a very grave, solemn, and serious demeanor. In this context, the suggestion is that Miss Betsey appears pompous and superior and evidently important.
In legal contexts, a "reversion" refers to the returning of property to a former owner or to a person who received the right to it when the former owner died.
"Saracen's Head in a Dutch clock..."See in text(Chapter 1 - I Am Born)
In Europe in the late Middle Ages, Saracen was the term used to denote a Muslim from the Middle East. The word "Dutch" in the passage is generally considered to be a misnomer for Deutsch, meaning German.
"supposititious..."See in text(Chapter 2 - I Observe)
The adjective "supposititious" means that something is based on wondering or supposing. Seeing that Peggotty is not happy to be taking Davy away and leaving his mother with Murdstone makes Davy wonder if he is being taken away for good and, if that is the case, if he would be able to find his way back home.
"Quinion,' said Mr. Murdstone, 'take care, if you please. Somebody's sharp..."See in text(Chapter 2 - I Observe)
The expression "somebody's sharp" serves as a warning that Davy might understand what the men are talking about. The suggestion is that Mr. Murdstone has designs on Mrs. Copperfield and perhaps her inheritance.
"bolting furtive gooseberries..."See in text(Chapter 2 - I Observe)
Generally, the verb "to bolt" states that something happens rapidly. So, in this context, he eats the gooseberries very quickly so that his mother doesn't notice.
A sun-dial is a device used to show the time of day by the position of the sun; it consists of a plate with markings like a clock and an object with a straight edge that casts a shadow onto the plate. As the sun moves, the shadow moves around the face of the plate, showing the passing of time and the present hour.
