The following sites have Yiddish dictionaries:

Harkavy Yiddish Dictionary  Yiddish Dictionary online

A .  B .  C .  D .  E .  F .  G .  H .  I .   J .   K .   L .  M .  N .  O .  P .  Q .  R .  S .  T .  U .  V .  W .  X .  Y .  Z . 

Lamed-vavnik (Yiddish): One of the thirty-six tzadikim in every generation in whose merit the world exists.

Lecha Dodi ("Come, my beloved"): A hymn recited as part of Kabbalat Shabbat.

Leckach:  (yid) Sweet cake (honey cake)

Lehavdil: 1. In contrast  2.Not to be mentioned together e.g. holy and impure 

Levaya: funeral

Levi ("Levite"; pl. Leviim): A descendant of Levi, the son of Jacob (excluding the priestly descendants of Aaron), whose role was to assist the Kohen in the Temple.

Leviathan: The name of an archetypal sea-creature, which is destined to wage battle against the Behemoth, only to be consumed by the righteous at the end of days.

Levush pl. levushim: Garment. One of the three primary "expressions" of the inner powers (the enclothed "limbs") of the soul (or "supernal sefirot")thought, speech and action. While the inner powers of the soul are seen to correspond to the sefirot in the world of Atzilut, the three "garments" of thought, speech and action are understood to correspond to the three lower worlds of Beriah, Yetzirah and Asiyahrespectively.

Lights: See sefirah.

Loshon hora: Slander.

Love (Ahavah): The spiritual state associated with the sefirah of chesed.

Lovingkindness (Chesed): The fourth of the ten sefirot, and the first of the emotive attributes within Creation.

Lowliness (shiflut): The spiritual state associated with the sefirah of malchut.

Lubavitch:  lit. 'town of love'; townlet in White Russia which from 1813-1915 was the center of Chabad Chassidism, and whose name has remained a synonym for it.

Lubavitcher Rebbe: Rabbi Menachem Mendel Schneerson (11 Nissan 1902 - 3 Tamuz 1994), the seventh Rebbe of the Chabad dynasty

Lubavitcher: 1. someone from the town of Lubavitch. 2. someone or something belonging to or of the Chabad movement.

Lulav ("palm branch"): One of the four species taken up and ritually shaken on the holiday of Sukkot. It is bound up with two other species--the hadas("myrtle branch") and the aravah ("willow branch"). These species are held together with the Etrog during the performance of the ritual.

Luria, Rabbi Isaac: See Ari.