Rashi on Numbers 5:21/רש"י על במדבר ה׳:כ״א

1בשבעת האלה [AND THE PRIEST SHALL ADJURE THE WOMAN] WITH AN ADJURATION OF CURSING — i.e., an oath which contains the curse.

2יתן ה’ אותך לאלה THE LORD MAKE THEE AN EXECRATION — i.e. that everybody will curse through thee (i.e., by mention of thy name), saying, “May misfortune come upon you just as it came upon Mrs. so-and-so!”

3ולשבעה [THE LORD MAKE THEE AN EXECRATION] AND AN OATH — This means, that everybody will swear through thee (i.e., by mention of thy name) — “If not (i.e., if I am not speaking the truth) may misfortune happen to me just as it happened to Mrs. So-and-so!” In a similar sense it states, (Isaiah 65:15) “and ye shall leave your name as an oath unto my chosen” which means that the righteous take an oath by mention of the punishment that came upon evil-doers. So, too, in reference to the blessing, does it state, (Genesis 12:3) “and through thee (i.e., by mention of thy name) shall bless themselves [all the families of the earth]”; (Genesis 48:20) “By thee shall Israel bless, saying, [God make thee as Ephraim and as Manasseh]” (Sifrei Bamidbar 14).

4את ירכך [WHEN THE LORD DOTH MAKE] THY THIGH [TO FALL, AND THY BELLY TO SWELL] — In uttering the curse that will befall her because of her sin he mentions the thigh before the belly (whilst in v. 22 the belly is stated to be affected first), because with it (the thigh) she began to sin (cf. Sotah 8b, 9b).

5צבה — Understand this as the Targum does: SWOLLEN.