The following sites have Yiddish dictionaries:

Harkavy Yiddish Dictionary  Yiddish Dictionary online

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Hadlakas haner: the lighting of candles in honor of Shabbos or Yom-Tov

Haftorah "conclusion": The Haftorah is the reading from the Prophets concluding the recitation of the Sabbath or festival Torah-portion.

Haggadah: Text recited at the Passover Seder, recounting the miracles of the Exodus from Egypt over 3000 years ago.

Hakafot: the processions around the bimah in the synagogue, conducted on Sukkot, Shemini Atzeret, and Simchat Torah while holding either the Torah-scroll or the four species.

HaKohen: Hebrew for 'the Priest' refers to someone who is a direct paternal descendant from Aaron

Halachah "The way" or "walking":  A general word referring to the entire system of Jewish law and ritual practice; plural halachot.

Hallel: "Praise"--Psalms 113-118 recited on Rosh Chodesh and certain festivals.

Haneirot Halalu ("These Lamps"): Haneirot Halalu is a liturgy recited after the kindling of the Chanukah lights.

Har Sinai: Mount Sinai

HaRav HaKodesh: The Holy Rabbi (see Rov).

HaShem:  Lit. The Name. Used as a reference for G-d's name

Hashgochah Pratis: Divine providence

Hashkafa: tracks of thinking in Jewish philosophy, approaches to religious Jewish life.

Haskalah:  1. Intellectualism of chassic thought  An adherent was called a maskil 2, a movement originating in 18th century Germany to acquire culture and customs of the outside world.

Havayah: A Holy Name of G-d.

Havdalah: Literally, "distinction"--the blessings recited over a cup at the conclusion of a Sabbath or festival to distinguish it from the ordinary weekdays that follow.

Hefsek Taharah: ("cessation of bleeding, indicating purity") A Hefsek Taharah is an examination through which a woman determines that her menstrual bleeding has ceased.

Hei: The 5th letter of the Hebrew alphabet.

Hemshach: In continuation, succession or following something previous etc. e.g. b'Hemshach. An opus of Chassidic Maamorim

Hergesh: Feeling, instinct

Hiddur: An adornment to a Mitzvah as in 'Hiddur mitzvah'; scrupulousness in performing a Mitzvah etc.

Hisbodedus: A form of meditation as a personal and private conversation with G-d.

Hiskashrus: Bond with the Rebbe, established by studying his teachings and following his directives

Hishtapchus hannefesh: The outpouring of the soul and its effort to rise out of the mire of sin, out of the shell of the evil spirit, the kelipah, and to reach the second stage, hishorerus, spiritual awakening.

Hislahavus: Religious enthusiasm, or flaming ecstasy.

Hishtalshelut:  The "order of creation" or the "order of development". See Seder HaHishtalshelut, cause and effect, 

Histalkus: Passing of a Tzaddik, especially one who taught mystical secrets (“penimiyus haTorah”)

Hisvaaduyos: The Rebbe’s unedited public addresses

Hod: lit. majesty':The fifth of the seven Divine middos, or attributes, and of their corresponding mortal middos, or spiritual emotions.

Hoshana Rabbah: The seventh day of the festival of Sukkos. Hoshanah Rabbah Last day of the intermediate days of Succos. It is

HY'D: Heb. HaShem Yimkom Domov HaShem should avenge their blood.