What does "royalty in nature" in Macbeth mean?

Question

In Macbeth (Act 3, Scene 1), Macbeth says about Banquo:

in his royalty of nature
Reigns that which would be feared.

What does "royalty of nature" mean here? Surely, Banquo is no "king of nature"?

Answer 1

The phrase means "royal nature" and refers to two things. First, it refers to Banquo's character and is a form of praise. For example, a few lines further down, Macbeth explains,

to that dauntless temper of his mind,
He hath a wisdom that doth guide his valour
To act in safety

Second, it refers to the prophecy that the three weyard sisters (called "witches" in the stage directions) gave in Act I, scene 3:

Thou shalt get kings, though thou be none

In other words, Banquo has a "royal nature" in the sense that his descendants will be kings. (This prophecy is not confirmed by the rest of he play: Banquo is murdered, after which his son Fleance disappears from the play, and at the end of the play Duncan's son Malcolm becomes the new king.)

Answer 2

In “his royalty of nature”, “nature” means “innate character or disposition”, and “royalty” is used in the sense:

royalty, n. 4. Kinglike or majestic character or quality.

_{Oxford English Dictionary.}

Then in the next line Macbeth gives us a metaphor in which Banquo’s character is compared to a kingdom, and the qualities that govern his character are compared to the ruler of the kingdom (“that which reigns”), which require Macbeth to fear him. The word “would” is used in this sense:

will, v. 3.b. figurative. Expressing a logical, legal, or moral requirement.

1600   W. Shakespeare Henry IV, Pt. 2 iv. i. 155   Then Reason will our hearts should be as good.

_{Oxford English Dictionary.}

Macbeth names the qualities that rule Banquo’s nature in the lines that follow: Banquo is brave (“’tis much he dares … that dauntless temper of his mind”) and calculating (“He hath a wisdom that doth guide his valour To act in safety”).

The metaphor of Banquo’s character being like a kingdom is suggested by the word “royalty” and perhaps we can take this as a pun, another sense of “royalty” being

royalty, n. 5.b. A royal domain; a kingdom, realm; a monarchical state.

_{Oxford English Dictionary.}

The OED’s first citation for this sense is from 1638, so if Shakespeare really had this sense in mind in Macbeth it would be an antedating.