The following sites have Yiddish dictionaries:

Harkavy Yiddish Dictionary  Yiddish Dictionary online

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Yabok: The name of the river which Jacob transversed upon entering Israel. In Kabbalah, an acronym for Yichud "unification", Berachah "blessing", Kedushah "holiness").

Yachid ("The Single One"):  G-d who is Omnipotent

Yakov Aveinu:  'Our father Jacob'

Yarzheit: anniversary of person's death.

Yavatz: Hebrew initials for Yaakov ben Tzvi. Name of Rabbi Yaakov Emden

Yayina shel Torah (יינה של תורה): lit. 'wine of Torah'. The homiletic style of Torah. Often alluded in the commentary of Rashi

Yechidah ("The singular one"): Yechidah is the highest of the five levels of soul, which will only manifest itself at the time of Mashiach. See soul.

Yechidei Segulah: Exceptionally holy and select individuals.

Yechidus: Special one on one time alone with a Rebbe

Yechzkel:  Ezekiel

Yehadut: Judaism

Yehoshua:  Joshua

Yehudim: Jewish people

Yemot Hamashiach: ("The days of Moshiach" -- Messianic era) See Olam Haba.

Yenika: Nourishment or attachment of impure forces-(kelipa) to hoilness. From the word to suckle

Yerushalmi: Talmud that was compiled in Palestine as opposed to the standard on that was compiled in Babylonia called the Bavli

Yesh me'ayin (Somethingness from nothingness): Yesh me'ayin is the process of creation ex nihilo.

Yesh (or yeshut): material reality or the state of independent self-consciousness; self, egotism, in Chassidic terminology. See Ayin

Yeshaya: Isaiah

Yeshivah, pl. Yeshivos: Torah academy for advanced students.

Yesod:  lit.'foundation':The sixth of the seven Divine middos, or attributes, and of their corresponding mortal middos, or spiritual emotions.

Yetzer HaRah:  Evil Inclination.

Yetzer Tov:  Good Inclination

Yetzer: lit. Inclination. It is Jewish belief that every Jew has both an evil and good inclination within him, that are at 'war' to see which of them the person will follow.

Yetzirah ("Formation"): Yetzirah is the third of the four worlds of Creation, wherein the ethereal ?substance? of Beriah is endowed with spirit and generic form; the consciousness of yesh m'yesh; the spiritual abode of the chayot; the origin of ruach in the soul of man.

Yeudim: Tidings

Yeush (yey-oosh): abandonment, despair

Yichud ("unification"): 1. A Yichud is a type of tikun in which one does not need to separate good from evil but rather focus one's consciousness on the inherent spiritual unity between two apparently disparate concepts. See birur. 2. (pl. yichudim) A specific spiritual exercise of this nature. 3.The spiritual state associated with the sefirah of Da'at.

Yid: A Jewish person

Yiddish: 1. Jewish 2. A language spoken by Jews.

Yiddishkeit: lit. 'Jewishness'; (Yiddish):Judaism; The Torah way of life.

Yirah ("fear"): the spiritual state associated with the sefirah of gevurah.

Yirmiya: Jeremiah

Yisroel: an additional name given to Jacob and the entire Jewish People.

Yisrael Sabba ("Israel the Elder" Aramaic):  the lower of the two primary partzufim which develop from the sefirah of chochmah (which together are referred to as the general partzuf of Abba).

Yitzchok: Isaac

YM'Sh: Heb. Yimach Shimoh V'Zichro Their name should be erased

Yom Hillula: The day of the passing of a Tzaddik who taught Pnimiyus HaTorah (the inner dimension of Torah); Hillula means literally “wedding,” for this day is regarded as a joyous occasion

Yom Kippur: The Day of Atonement, the most holy day of the Jewish year.

Yom Suf: 'sea of reeds'.

Yom Tov ("A good day"): festive holidays on which, with certain exceptions, weekday work is prohibited just as on Shabbat.

Yom-Tov Sheni shel Galuyos: One of the days which only in the Diaspora is appended to each of the three Pilgrim Festivals.

Yud Shevat: The 10th day of the month of Shevat, the day of the Histalkus of the sixth Rebbe of Chabad, when the Rebbe became the Rebbe

Yud: the 10th letter of the Hebrew alphabet.

Yud-Beis and Yud-Gimmel Tammuz:: the twelfth and thirteenth of the month of Tammuz' Chassidic festival marking the anniversary of the release of the Rebbe Rayatz from incarceration and exile in Stalinist Russia in 1927.

Yud-gimmel middos: The thirteen attribtes of Mercy, the thirteen tufts of the "beard" of Arich Anpin

Yud-Tes Kislev:: the nineteenth of the month of Kislev' Chassidic festival celebrating the liberation of the Alter Rebbe from capital sentence and imprisonment in Petersburg (1798), after having been slandered to the czarist authorities by his opponents.

Yumtak: (heb ויומתק) lit. "sweetened" 1. Fits 2. Makes sense 3. Further proven 4.enriched