A sandek or sandak (Hebrew: סנדק "companion of child") is a person honored at a Jewish brit milah (circumcision) ceremony, traditionally either by holding the baby boy on the knees or thighs while the mohel performs the brit milah, or by handing the baby to the mohel.
[3] The role is distinct from that of the kvater who carries the baby in Ashkenazi ceremonies, based on the Yiddish word for godfather.
A special seat, usually richly decorated, was prepared in the synagogue for the sandik, and if the circumcision happened on a day of Torah reading, he was entitled to receive an aliyah.
Rabbinical authorities (for instance, Rabbenu Peretz and Judah the Hasid) decreed that the privilege should not be given more than once to the same man in the same family, neither should it, unless unavoidable, be given to women.
[11] The Aruch Hashulchan notes, though, that the custom in many locales is that the rav (rabbi) of the city serves as the sandek for all the baby boys.
The Aruch Hashulchan justifies this practice by comparing the local rav to the kohen gadol (high priest), who had the right to offer a korban (sacrifice) or incense any time he desired.
Rabbi Yissocher Frand relates that Rav Yaakov Yitzchak Ruderman (the rosh yeshiva (dean) of Yeshivat Ner Yisrael) also served as the sandek for countless baby boys.
[1] The sandek also wore the tallit (prayer shawl) and held the baby on a pillow while the mohel completed the circumcision.