Rashi on Numbers 5:30/רש"י על במדבר ה׳:ל׳

1או איש — The word או here has the same meaning as in the phrase (Exodus 21:36): או נודע, “If it be known” (cf. Rashi on that verse and our Note thereon) — that is to say: if the man is a jealous man, then just on account of this, he shall present the woman [before the Lord and then the priest shall execute upon her all this law].”