trial balloon vs trial

trial balloon and trial both are nouns.

Word	Noun	Adjective	Verb	Adverb
trial balloon	Yes	No	No	No
trial	Yes	No	No	No

As nouns, trial is a hypernym of trial balloon; that is, trial is a word with a broader meaning than trial balloon:

Other hypernyms of trial balloon include test, trial run, tryout.

trial balloon (noun)	trial (noun)
a balloon sent up to test air currents	the act of testing something
a test of public opinion	(law) the determination of a person's innocence or guilt by due process of law
	the act of undergoing testing
	trying something to find out about it
	an annoying or frustrating or catastrophic event
	(sports) a preliminary competition to determine qualifications