weather balloon

plural of trial balloon

(aeronautics, 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.

a club for ballooning enthusiasts

plural of barrage balloon

mail (usually for weight reasons in the form of a postcard) carrying the name of the sender by means of an unguided hydrogen- or helium-filled balloon.

plural of balloon flower

plural of balloon clock

plural of thought balloon

(comics) A shape like a speech bubble, but conveying thought, typically emanating from the thinker by a path of small circles.