(obsolete) An honest and truthful person.

(obsolete) Exposing the truth; revealing; illuminating.

(informal, medicine) A psychoactive medication, especially one administered by injection, which supposedly renders a person cooperative and disposed to respond honestly to questions.

Synonym of truth serum

(idiomatic) Any facts or true statements at all. / (idiomatic) A small piece of true or useful information.

plural of grain of truth

(politics) A group of people who attend political meetings etc. in the guise of ordinary citizens in order to promote a particular viewpoint.

plural of truth squad

(colloquial) That is very true; I agree (often with a gloomy or pessimistic tone).

plural of hard truth