What do we call the target of an appositive?

Question

From Wikipedia (emphasis mine):

Apposition is a grammatical construction in which two elements, normally noun phrases, are placed side by side so one element identifies the other in a different way. The two elements are said to be in apposition, and one of the elements is called the appositive, but its identification requires consideration of how the elements are used in a sentence.

I'm reminded of the parts of a definition. By this analogy, if the apposition is the definition, then the appositive is the definiens. What then is the term for the equivalent of the definiendum?

Specifically, I am interested in the parentheses which appear in contracts and other legalese:

• Tenant has thirty (30) days to . . .
• . . . twenty-five million dollars ($25,000,000) . . .

Some StackExchange user called these constructs "reformulatory appositive parenthetical" but I cannot find any other reference of this term. Nonetheless, in the abscence of my finding of a suitable technical term for these constructs, I think that's a suitable way of describing these.

• thirty = ?
• (30) = appositive parenthetical
• twenty-five million dollars = ?
• ($25,000,000) = appositive parenthetical

Answer 1

A few terms have been used:

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With dependency relations, an appositive is often considered to be a dependent (child) in apposition to its parent, sometimes called the phrase's head.

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The referent of an apposition is usually the thing to which both terms refer. For example, a quantity of money would be the referent of both "twenty-five million dollars" and "$25,000,000". However, the former is sometimes called the referent of the appositive. For example:

The son’s name is a non-restrictive appositive because it is useful, but unnecessary information; the name does not modify its referent in a way that changes the meaning of the sentence. ("Appositives", American University, Academic Support Center, Writing Lab, updated 2009, https://www.american.edu/provost/academic-access/upload/appositives.pdf)

Another example:

The phrase “set off” is significant, because a pair of commas separate the parenthetical apposition from its referent noun by a pair of commas. (Mark Nichol, "The Difference Between Appositives and Descriptions", Daily Writing Tips, https://www.dailywritingtips.com/the-difference-between-appositives-and-descriptions/)

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Another possibility is anchor, as in this document ("Appositive Relative Clauses", LOT Summer School 2005, Universiteit Leiden, The Syntax and Semantics of Nominal Modification, 17 June 2005). Note, however, that that document uses "appositive" differently from how you seem to be using the term.

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The term antecedent is addressed in another answer.

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Finally, I'll just add that I like target. It is clear, simple, unlikely to be confused with other grammar terms, and makes a nice analogy with similar relationships. It hasn't been used in this context as far as I'm aware, though.