פּירוש אויף דברים 5:17

ולא תנאף AND THOU SHALT NOT COMMIT ADULTERY — The term ניאוף, “adultery”, is technically only applicable in the case of a married woman.

NEITHER SHALT THOU BEAR ‘EID SHAV’ (VAIN WITNESS)¹⁷²In Exodus 20:13, the verse reads: Thou shalt not bear ‘eid shaker’ (false witness). Ramban explains that the admonition here prohibits bearing such false testimony even when it cannot possibly harm the neighbor at all and is consequently “vain” and worthless in court. The prohibition in Exodus, on the other hand, concerns the kind of false testimony which aims to really harm the other person. Thus the verse here explains the full extent of the admonition. AGAINST THY NEIGHBOR. He explained this in order to prohibit even [false] meaningless testimony that will cause no harm at all to his neighbor in court, as, for example, if he testifies, “So-and-so said he will give a hundred [dinars] to that person, but did not obligate himself to do it” [such false testimony is consequently in “vain” and we are prohibited from so doing]. For the term shav [in the above admonition, as elsewhere] signifies “vain, worthless” talk.

עד שוא, “a vain witness.” If someone testifies against someone whom he had seen perform a crime deliberately, but his testimony is not supported by a second witness or there are two witnesses but the person was not warned about the consequences of his crime before performing it, he is not to come forward to bring a charge he knows that a conviction could not be obtained under these circumstances.