This means that just like the father and mohel, if the sandak attends prayer services prior to the bris, he will cause the entire congregation to automatically join in the celebration of his holiday, to the point they will not recite the "Tachanun" (supplication) prayer, which beseeches God to help us in our hour of suffering. Who can possibly be suffering on a holiday?
It is sometimes asked if the baby's father can serve as the sandak. He may!
Contary to the Ashkenazic custom mentioned below about not repeating sandak in a family, a father is the only person who CAN serve in this role multiple times for his own sons. I remember attending a bris in Israel where the baby was the 10th boy in the family (talk about having it down to a system!), and the father was being sandak for the third or fourth time. The reason? They had honored everyone else already once (who might play ths role otherwise) and as it's the father's mitzvah to be as involved as possible in the bris, the father chose to play the role of Sandak to fulfill his responsibility in the best way he could.
Where does the word SANDAK come from?
Some people think it comes from Greek:
Although circumcision is probably the most ancient of all the Jewish rites that are practiced today, neither of these two words is anywhere near as venerable. The older of the two, sandak, is a Hebrew loan word from Greek, as easily can be seen from its earliest appearance in Jewish sources in the 13th-century midrashic anthology Yalkut Shimoni, where it occurs as sandakos - סנדיקוס, with the Greek first-declension, nominative-case singular ending. This is curious, since nearly all Greek borrowings in old Hebrew date to the pre-Islamic period, when Greek was the spoken language of the eastern Mediterranean world.
Presumably, then, sandakos was in use among Jews for hundreds of years before this but simply left no record. Its etymology is from syndikos, i.e., an advocate in a trial, and also, a backer or supporter. Syndikos was a word commonly used in Greek to translate the Latin patronus, which also could mean either a legal counsel or a
social patron — and just as the Roman patronus had a moral if not legal obligation to assist whomever the person to whom his patronage is extended, so the Jewish sandak was originally thought of, it would seem, as responsible for the circumcised child throughout his life. For this reason, the sandak was traditionally chosen from among the close friends or relatives of the parents of the child, with whom he was expected to maintain a lifelong bond.
But why should we assume this Jewish role was borrowed from the Greeks? Especially when they (or at least Antiochus Epiphanes - starting 4th paragraph) banned circumcision? (This tradition has been around a lot longer than this new theory)
WHAT IS THE JEWISH SOURCE FOR THE SANDAK?
One approach is that סנדק is actually an acronym for סנגור נעשה דינו קטיגור - which means that the "defender becomes the prosecutor." This idea stems from the Kabbalistic work - The Zohar (p. 255) - which explains "When the little boy is undergoing his surgery, the sitra achra is broken down and has no power - because the bris becomes a litigator against him on behalf of Israel."
In other words, in a kabbalistic sense, the sitra achra is always trying to find flaws in the activities of the Children of Israel, constantly making them the defendants before God. But the bris is so powerful, and the helpful role the Sandak plays in protecting the baby and allowing the mohel to do his job properly, changes the keepers of the faith from being defendants against this evil spirit to being prosecutors against him. "How dare you suggest we are not keeping the law and following God's commandments when you see we begin at the very beginning of life with the covenant of our faith, the covenant of circumcision?"
Not as exciting
Yashresh Yaakov suggests that the numerical value of the word Sandak = 218, if you add the values, סנדק =
60 + 50 + 4 + 100 + the 4 letters of the word = 218, which refers to a "ריח ניחוח" - a sweet fragrance from a spice offering (ריח = 218). This most likely relates to the idea that the Sandak is compared to one who brings such an offering when he is holding the baby on his lap during the bris.
No Matter the Source...
... The Sandak is a great honor. It is often given to the baby's grandfather or great-grandfather, if the baby is blessed to have one.
The role can not be shared during a bris.
Amongst Jews of Ashkenazic descent there is a custom for parents not to reuse a sandak for another son of theirs. Essentially, the idea is to "spread the wealth around" (to coin a phrase) and give others a chance to play this highly significant and symbolic role.
Amongst Jews of Sephardic descent (Spain, North Africa and Middle East), the same person might be sandak every time, if the individual is a highly respected dignitary, such as a "Hakham" or great rabbi, or even the patriarch of a family.