• WordNet 3.6
    • n semicolon a punctuation mark (`; ') used to connect independent clauses; indicates a closer relation than does a period
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Webster's Revised Unabridged Dictionary
    • n Semicolon The punctuation mark [;] indicating a separation between parts or members of a sentence more distinct than that marked by a comma.
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Century Dictionary and Cyclopedia
    • n semicolon In grammar and punctuation, the point (;). It is used to mark a division of a sentence somewhat more independent than that marked by a comma. (See punctuation.) In old books a mark like the semicolon was often used as a mark of abbreviation, being in fact another form of the abbreviative character ȝ, z, in oz., viz., etc.: thus, “Senatus populusq; Romani”; and in Greek the semicolon mark (;) is the point of interrogation.
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Chambers's Twentieth Century Dictionary
    • Semicolon the point (;) marking a division greater than the comma
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In literature:

It was the big thing out of life he had read to her, not sentence-structure and semicolons.
"Martin Eden" by Jack London
The colon, semicolon, and note of admiration, were produced some time after the others.
"English Grammar in Familiar Lectures" by Samuel Kirkham
I find the semicolon very useful for cumulative effects.
"Balloons" by Elizabeth Bibesco
Then he read aloud, with a comma or semicolon between each, a dozen or twenty titles.
"In Luck at Last" by Walter Besant
A semicolon (;) between parts that are subdivided by commas.
"The Handy Cyclopedia of Things Worth Knowing" by Joseph Triemens
The semicolon is used to denote a degree of separation greater than that indicated by the comma, but less than that indicated by the colon.
"Punctuation" by Frederick W. Hamilton
Of course, this rule must be qualified by the rules for the stronger points, especially by those for the semicolon and the colon.
""Stops"" by Paul Allardyce
Use the semicolon to separate the clauses of a compound sentence that are long or that are not joined by conjunctions.
"Practical Grammar and Composition" by Thomas Wood
A semicolon might be used, if a semicolon were not used within the second independent element.
"English: Composition and Literature" by W. F. (William Franklin) Webster
The four chief punctuation points are the comma, semicolon, colon, period.
"Social Life" by Maud C. Cooke

In news:

Semicolons and Exclamation Points' New Enemy in Punctuation Wars: Cormac McCarthy.
Modeled on the sparse style of James Joyce , Cormac's books are free of quotation marks, semicolons and most other grammatical marks.
Modeled on the sparse style of James Joyce, Cormac's books are free of quotation marks, semicolons and most other grammatical marks.
As a college newspaper editor who wades through a constant torrent of submissions of questionable grammatical integrity, I applaud your appreciation of the semicolon (Week in Review, Nov 7).

In science:

This spreadsheet has been tested on the spreadsheets calc, Microsoft Excel, and Gnumeric. Note that all semicolons (;) must be replaced by commas (,) for Excel and Gnumeric.
TellTable Spreadsheet Audit: from Technical Possibility to Operating Prototype
However, in the literature on GR, the word “diffeomorphism” is often used as equivalent of the transformation (1) (the semicolon “;” means a covariant derivative) and in our article the latter meaning is employed.
Diffeomorphism Invariance in the Hamiltonian formulation of General Relativity
In the following example production, a statement can be, among other things, an error terminated by a semicolon.
LR(1) Parser Generation System: LR(1) Error Recovery, Oracles, and Generic Tokens
Here and further, we sometimes write s after the semicolon to explicitly indicate that the function depends on the chosen first switching time s as on a parameter.
Symmetric periodic solutions of parabolic problems with hysteresis
The partial derivative w.r.t. xα is indicated with ∂α or with a comma, for example we have: uβ ,α = ∂αuβ . • The covariant derivative w.r.t. xα is indicated with ∇α or with a semicolon, for example we have: uβ ;α = ∇αuβ .
Backreaction and the Covariant Formalism of General Relativity