Hebrew: Righteous One
According to Gershom Scholem, in his essay Tsaddik: THE RIGHTEOUS ONE ("On the Mystical Shape of the Godhead", Schocken Books, 1991), "the religious ideals of Judaism have crystallized around three ideal human types that carry special significance: the Tzaddik, the righteous man; the Talmid Hakham, the scholar of sacred texts; and the Hasid, the pious person."
In his essay, Herr Scholem (who, by the strange laws of genius, found the C. S. Lewis to his Tolkien, or Nietzsche to his Wagner, in Walter Benjamin), charts the development of the relationship between Tzaddik and Hasid, describing how "righteous one" originally meant a person who followed the letter of the Law, who lived his life in perfect conjunction with the outer (and lower) manifestation of the Torah. As opposed to a Hasid, who sought to embody the spirit of the Law, who might make an utter fool of himself in order to embody a minute aspect of the Gift of Moses, or spend his whole life seeking to perfect even a minor quality of its inner meaning.
The Tzaddik, then, was what in Islamic terminology is called Shari’ a, or one who simply has faith in what has been passed down to him, e.g., think of your basic, respectable, church-going citizen. They surely believe, even ardently, in what their pastor or priest abdicates, but in their spiritual development, they rarely go beyond acting correctly (giving tithes or volunteering at a shelter from time to time). Their spirituality is at the level of what is currently deemed "religious." It has little revelation, little personal receiving within it -- which does not make it false, only somewhat shallow. (See the write up under tarekh for a further discussion on these particular levels of faith.)
But when Hasidism rose up in 17th century Poland, the terms Hasid and Tzaddik went through a (Scholem argues necessary) polarization. The Tzaddik, or Righteous One, became the teacher, the leader, he who carries the pain and suffering and spiritual progress of his flock on his own shoulders, while the Hasid became the term for follower, or faithful member of the congregate.
There is also a Kabbalistic definition of Tzaddik, where the term comes to signify the Path of the Divine Flow, that is, a Divine Phallus, bringing the gift of Life, the essence of what Living is, down to the Shekinah (who here means the lower Daughter, the pool of phenomena, the "surface of the deep" mentioned in Genesis 1:2).
In the Kabbalah, the Tzaddik is found in the central column in the tree of life (see my diagram under that node), and also in the 9th sephiroth, Yesod, "The foundation of the world". It is as the foundation that the Tzaddik "constitutes the harmonious conciliation of all the potencies located above it; {and as} the symbol of the Sabbath {it} provides a link between the themes of conciliation and repose, in which "all effects are fulfilled", and {becomes} that of the source or foundation of all souls." (ibid, pp 95).
We may then correspond the Tzaddik, in so far as we are speaking Kabbalistically, with Budhi, (Sanskrit: the drop of the divine essence which resides in all living creatures, from lowest to highest), only Scholem goes further than just making Tzaddik the path or sphere of the activity of the soul, he develops it into the source from whence "all souls fly out." The "treasury of souls" from where all souls come.
Is it then some sort of portal, a widow through which heaven's creatures are brought into the world of matter? In that case, can it symbolize a certain type of action, or acting, by which souls may enter this world with some measure of heavenliness still inherent in them? According to Bapak Muhammad Subuh, the parents of a child have a direct effect not only in the creating of the outer constitution of the child, but also in the forming of their soul, the very state of their offspring's character. He urges, in his talks, for a man and a woman to approach the procreative act in a state of worship and surrender to the Creator (who, incidentally, he refers to as Allah), in order that the soul of the child there conceived may be that of a high being, rather than being influenced by (or made out of) coarse carnal desire or even the need to reconcile an argument over the credit card bill.
I have no textual evidence to support this idea, but if we look at the evolution of the word Tzaddik, it does make sense that this "portal" or "treasury of souls" be bound to righteousness, and what is righteousness if not a way of acting, or a characteristic of a human when that human is dealing with the outside world?
Orthodoxy, after all, is little more than conjecture without a sound orthopraxy. One must preach (that is, seek to embody) something that is not only correct, but practicable.
"In guiding students on the ultimate path of awareness," writes Rabbi David A. Cooper, "the Talmud says in the name of Rabbi Phinehas ben Jair, "Study leads to precision, precision leads to watchfulness, watchfulness leads to cleanliness, cleanliness leads to restraint, restraint leads to purity, purity leads to saintliness, saintliness leads to humility, humility leads to fear of sin, fear of sin leads to holiness, holiness leads to the holy spirit, and the holy spirit leads to life eternal."
This is one version of the path of the Tzaddik.
Sources:
"On The Mystical Shape of the Godhead", Gershom Scholem
The Complete Recorded Talks of Bapak Muhammad Subuh Sumohadiwidjojo, Vol 5
"God Is A Verb", David A. Cooper