C. F. Keil and Franz Delitzsch on Proverbs 14:25

Pro 14:25 25 A witness of truth delivereth souls;      But he who breathes out lies is nothing but deception.

When men, in consequence of false suspicions or of false accusations, fall into danger of their lives (דיני נפשׁות is the designation in the later language of the law of a criminal process), then a tongue which, pressed by conscientiousness and not deterred by cowardice, will utter the truth, saves them. But a false tongue, which as such (vid., Pro 14:5) is a יפח כזבים (after the Masora at this place ויפח, defective), i.e., is one who breathes out lies (vid., regarding יפיח at Pro 6:19), is mere deception (lxx, without reading מרמּה [as Hitzig does]: δόλιος). In Pro 12:17 מרמה is to be interpreted as the object. accus. of יגיד carried forward, but here to carry forward מצּיל (Arama, Löwenstein) is impracticable - for to deliver deceit = the deceiver is not expressed in the Hebr. - מרמה is, as possibly also Heb 12:16 (lxx δόλιος), without אישׁ or עד being supplied, the pred. of the substantival clause: such an one is deception (in bad Latin, dolositas), for he who utters forth lies against better knowledge must have a malevolent, deceitful purpose.