出典:Wiktionary
trial-balloon (複数形 trial-balloons)
Calque of French ballon d’essai (“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; (比喩的に) prospective action to test acceptance”): ballon (“balloon”), essai (“trial, try; assay”).[1]
trial balloon (複数形 trial balloons)