the

Used before a noun phrase, including a simple noun

I’m reading the book Mary reviewed. (Compare I’m reading a book Mary reviewed.)

You live on Main Street, don't you? You know, you should tell the mayor the street needs cleaning.

Used before a noun phrase, including a simple noun

No one knows how many galaxies there are in the universe.

God save the Queen!

Used before a noun phrase, including a simple noun

No one in the whole country had seen it before.

I don't think I'll get to it until the morning.

Used before a noun phrase, including a simple noun

A stone hit him on the head. (= “A stone hit him on his head.”)

(informal) How's the wife? (= "How is your wife?")

Used before a noun phrase, including a simple noun

How's the Sal today?

With a comparative or with more and a verb phrase, establishes a correlation with one or more other such comparatives.

The hotter(,) the better. (comma usually omitted in such very short expressions)

The more I think about it, the weaker it looks.

With a comparative, and often with for it, indicates a result more like said comparative. This can be negated with none.

It was a difficult time, but I’m the wiser for it.

It was a difficult time, and I’m {none - not any} the wiser for it.

Beyond all others.

We went the furthest under her leadership.

They trusted him the most.

For each; per.

valued at half a pound the bushel; paying seven dollars the year interest

Next morning I was up at an early hour, to see the market held near the water gate. The beef was excellent: but at the high prices of ten-pence and one shilling the pound; mutton at the same price; fowls a dollar the couple, and showing “more feathers than flesh.”