trial balloon

/T R AY1 AH0 L B AH0 L UW1 N/
noun
  1. 1

    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.

  2. 2

    An idea, suggestion, or prospective action, product, etc., offered to an audience or group in order to test whether it generates acceptance or interest.

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Source: https://en.wiktionary.org/wiki/trial%20balloon