trial-balloon

Noun

trial balloon (plural trial balloons)

1. (historical) A small balloon released into the sky to determine the direction and tendency of winds in the upper air before a manned ascent in a larger balloon; a ballon d'essai.
   • For many weeks in succession the little trial balloons thrown up to show the course of the wind were driven back upon the shores of France.1870, F[ulgence] Marion, “The Necrology of Aeronautics”, in Wonderful Balloon Ascents: Or, The Conquest of the Skies. A History of Balloons and Balloon Voyages. From the French (Illustrated Library...
2. (figuratively, idiomatic) An idea, suggestion, or prospective action, product, etc., offered to an audience or group in order to test whether it generates acceptance or interest.
   • "The originality of the plan and views of the author [Jean Baptiste Bory de Saint-Vincent], and, above all, the perfect independence of its execution," are, according to the narrator in the Bulletin, the chief features of this new production; and the summary sketch of it which has been published...1826 July, “Art. VI.—Remarks on M. le Colonel Bory de St-Vincent’s Proposed Species of the Genus Homo.”, in David Brewster, editor, The Edinburgh Journal of Science, volume V, number I, Edinburgh...

   Synonyms:

   ballon d'essai, feeler