Numbers 5:20

20 But if being a married woman thou hast transgressed, or been polluted, and any one has lain with thee, beside thy husband:

Numbers 5:20 Meaning and Commentary

Numbers 5:20

But if thou hast gone aside to another instead of thy
husband
Gone aside from the paths of modesty and chastity, and betook herself to another man's bed instead of her husband's:

and if thou be defiled,
by committing adultery:

and some man hath lain with thee beside thy husband;
these phrases are all synonymous, and a heap of words are made use of to express the sin, and that there might be no evasion of it, and that it might be clear what was intended, this being said on oath.

Numbers 5:20 In-Context

18 And the priest shall cause the woman to stand before the Lord, and shall uncover the head of the woman, and shall put into her hands the sacrifice of memorial, the sacrifice of jealousy; and in the hand of the priest shall be the water of this conviction that brings the curse.
19 And the priest shall adjure her, and shall say to the woman, If no one has lain with thee, and if thou hast not transgressed so as to be polluted, being under the power of thy husband, be free from this water of the conviction that causes the curse.
20 But if being a married woman thou hast transgressed, or been polluted, and any one has lain with thee, beside thy husband:
21 then the priest shall adjure the woman by the oaths of this curse, and the priest shall say to the woman, The Lord bring thee into a curse and under an oath in the midst of thy people, in that the Lord should cause thy thigh to rot and thy belly to swell;
22 and this water bringing the curse shall enter into thy womb to cause thy belly to swell, and thy thigh to rot. And the woman shall say, So be it, So be it.

The Brenton translation of the Septuagint is in the public domain.