John Gill Commentary Numbers 5:21

"then the priest shall cause the woman to swear with the oath of cursing, and the priest shall say unto the woman, Jehovah make thee a curse and an oath among thy people, when Jehovah doth make thy thigh to fall away, and thy body to swell;" — Numbers 5:21 (ASV)

Then the priest shall charge the woman with an oath of
cursing
An oath which has a curse annexed to it, if taken falsely, which was to be pronounced upon the woman if guilty:

and the priest shall say unto the woman ;
pronouncing the imprecation or curse upon her, she having taken the oath, should she be guilty of the crime suspected of, and she had swore concerning:

the Lord make thee a curse, and an oath among the people ;
accursed according to the oath taken; or let this be the form of an oath and imprecation used by the people, saying, if I have done so and so, let me be accursed as such a woman, or let not that happen to me, as did to such a woman, so Jarchi:

when the Lord doth make thy thigh to rot, and thy belly to swell ;
upon drinking the bitter waters; but though these things followed upon that, yet not as the natural cause of them, for they are ascribed to the Lord, and to a supernatural and miraculous power of his, which went along with the drinking of them.