extern

plural externs

1. A person affiliated with an institution in a lesser capacity, for example, as a non-resident or as a part-time affiliate.
   1. A day-scholar.
2. Outward form or part; exterior.

1. obsoleterareExternal; outward; not inherent

   For if the ſoul of man vvere emancipated by virtue, it vvould not need any regulation or monition, beſides that of its invvard Tribunal; vvhich becauſe ſin does uſurp upon, has ſome relief from thoſe extern adjuments.

   1663, Edward Waterhous[e], chapter XIV, in Fortescutus Illustratus; or A Commentary on that Nervous Treatise De Laudibus Legum Angliæ, Written by Sir John Fortescue Knight, […], London: […] Tho[mas] Roycroft for Thomas Dicas […], →OCLC, page 214

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   Heaven is my judge, not I for love and duty, / But seeming so, for my particular end, / For when my outward action doth demonstrate / The native act and figure of my heart / In complement extern, 'tis not long after / But I will wear my heart upon my sleeve / For daws to peck at.

   c. 1603–1604 (date written), William Shakespeare, “The Tragedie of Othello, the Moore of Venice”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene i]

plural externs

1. computingIn the C and C++ programming languages, a variable that can be separately declared in many places, all of them referring to the same variable.

   Finally, get rid of the two function declarations and two externs that we added at the top of TEFIL.CPP so that we could support file_open().

   1995, Martin L. Rinehart, Learn C++ Today!, page 552

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   This is probably the big thing with C++, the more you can avoid global concepts and nasty externs the better, an object/class should be totally self-contained.

   2018, Brian Beuken, The Fundamentals of C/C++ Game Programming