simple past tense and past participle of ground truth

The absolute truth; used as an emphatic asseveration that one is not lying.

plural of tell-truth

(obsolete) An honest and truthful person.

(obsolete) Exposing the truth; revealing; illuminating.

plural of grain of truth

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

(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).