What is Discredit?

Legal Definition
Practice, evidence. To deprive one of credit or confidence.

2. In general, a party may discredit a witness called by the opposite party, who testifies against him, by proving that his character is such as not to entitle him to credit or confidence, or any other fact which shows he is not, entitled to belief. It is clearly settled, also, that the party voluntarily calling a witness, cannot afterwards impeach his character for truth and veracity. 1 Moo. & Rob. 414; 3 B. & Cress. 746; S. C. 10 Eng. Com. Law R. 220. But if a party calls a witness, who turns out unfavorable, he may call another to prove the same point. 2 Campb. R. 556 2 Stark. R. 334; S. C. 3 E. C. L. R. 371 1 Nev & Man. 34; 4 B. & Adolph. 193; S. C. 24 E. C. L. R. 47; 1 Phil. Ev. 229; Rosc. Civ. Ev. 96.
-- Bouviers Law Dictionary
Legal Definition
To destroy or impair the credibility of a person; to Impeach; to lessen the degree of credit to be accorded to a witness or document, as by impugning the veracity of the one or the genuineness of the other; to disparage or wcaken the reliance upon the testimony of a witness or upon documentary evidence, by any means whatever.
-- Black's Law Dictionary
Legal Definition
To injure one’s credit or reputation; to refuse credence; to distrust. See 84 Cal. 573, 24 Pac. 313.
-- Ballentine's Law Dictionary