The text under discussion is לֹא-תַעֲנֶה בְרֵעֲךָ עֵד שָׁקֶר (Exodus 20:16). The pertinent word, שָׁקֶר [sheqer (pronounced sheh'-ker)], is analyzed by Strong as "an untruth; by implication, a sham (often adverbial):--without a cause, deceit(-ful), false(-hood, -ly), feignedly, liar, + lie, lying, vain (thing), wrongfully".
Brown-Driver-Briggs' Hebrew Lexicon offers the following:ׁ
1) lie, deception, disappointment, falsehood
1a) deception (what deceives or disappoints or betrays one)
1b) deceit, fraud, wrong
1b1) fraudulently, wrongfully (as adverb)
1c) falsehood (injurious in testimony)
1c1) testify falsehood, false oath, swear falsely
1d) falsity (of false or self-deceived prophets)
1e) lie, falsehood (in general)
1e1) false tongue
1f) in vain
Needless to say, both Rabbinic and Christian exegesis (and eisegesis!) have had plenty to say about this injunction; however, there is no doubt that a more general ethical implication of truth-telling can hardly be excluded from what was certainly in origin, as Dhammanando Bhikkhu has pointed out, a legal formula.