Commentary for Numbers 25:3

פעור — It was so named because they bared (פער) their anus and relieved themselves before it: this was its ceremonial rite (Sanhedrin 60b).

ויחר אף, the pestilence being proof of G’d’s anger.

ויצמד ישראל לבעל פעור, “Thus Israel attached itself to Baal-peor.” The word ויצמד is from the same root as צמד בקר, “a yoke of oxen.” The meaning of the expression is that man and woman coupled together. There is a difference in meaning between the expression הצמדה and דבקות, although both express a state of togetherness, union, almost. הצמדה is a less intimate relationship, a looser coupling than דבקות. If the Torah had written here וידבק ישראל לבעל פעור, G’d forbid, this would have been such a grave sin that it could not have been repaired. This consideration is also reflected in the sages saying in Sanhedrin 64 that whereas the attachment of the Israelites to the deity בעל פעור was comparable to a lid over a pot, the attachment of the Israelites to their G’d (Deut. 4,4) is described as ואתם הדבקים בה' אלוקיכם, “you who cleave to the Lord your G’d,” i.e. a far closer attachment than that of the lid to the pot. The term דבקות when applied to two entities implies that they are so alike and clinging to each other as to be interchangeable. According to a Baraita the term ויצמד is related to צמידים — a bracelet worn by a woman (worn loosely but not attached to the body), while ואתם הדבקים indicates a tight bond.