Labefaction: shaking, weakening and/or downfall;  impairment, especially of moral principles or civil order [L. labefactus, labefacere (“to cause to totter”; “shake”) from labare (“to totter”) + -facere (“to make”) + -ion]

Labile: unstable; liable to change [from L. labi, (“to slip or fall”)]

Labrose: thick-lipped [L. labrosus, from labrum (“lip”)] 👄

Laevorotatory or Levorotatory: counter- or anti-clockwise (opp. Dextrorotatory) [L. levo from laevus (“left”) + rotatiō] 🕰️

Lampadedromy: foot race with lighted torches, esp a relay race passing the torch from runner to runner (Anc. Greece: a race in honor of Prometheus in which the contestants ran bearing lit torches, the winner being the first to finish with his torch still lit) [Gk. lampein (“to shine”) + –dromos (“a running”)]

Lamprophony: speaking in a clear loud voice [Gk. lampróphónos (“clear-voiced”) from lamprós (“clear”; “distinct”) + -phone (“sound”) + -y]

Languescent: becoming tired or languid [from L. languescere (“to become faint”)]

Lapidate: stone to death [L. lapidare (“to stone”), from lapid-, lapis (“stone”) + -ate]

Latebricole: living in holes (OU) 🕳️

Latibulise: to hibernate (OU)

Latifundian: rich in real estate [ L. latus, (“spacious”) + -fundus, (“farm”, (“estate”)] (Latifundium was a large agricultural estate in Ancient Rome)

Leman: paramour; lover; inamorata [from OldEng. lēofmann (“lover”); (“sweetheart”); equiv. to lief +‎ –man (“beloved person”)]

Lenitic or Lentic: living in quiet or still waters [L. lenitas (“mildness”) + -ic] (cf. Lotic: living in actively moving waters)

Lepid: charming; elegant; amiable [from Gk. lepid-, lepis (“scale”?), from lepein]

Lestobiosis: living by furtive stealing; the act of pilfering food, especially of ants 🐜 [Gr. lestes, (“robber”) +–biosis, (“manner of life”)]

Loganamnosis: a mania for trying to recall a forgotten word or words [Gk. log (“word”) + -amnosis (?) perhaps from –amnesia (“memory”)]

Lucifugous: avoiding daylight or light altogether [ from L. lucifugus, from luci- + -fugus (from fugere (“to flee”) + -al +-ous]

Lucripetous: money-hungry (OU) 💰

Luctiferous: sad and sorry [L. luctifer (“mournful”) from luctus (“sorrow”) + -fer (-ferous) + –ous]

Ludification: derision; mockery [from L.  ludificatio, from ludificare (“to make sport of”), from ludus (“sport”) + -ficare (“to make”, in comparative)]

Lurdane: stupid, dull and lazy; a sluggard [MidFr. lourdin (“dullard”), from lourd (“heavy”)]

Lypophrenia: a vague feeling of sadness, seemingly without cause [OU. ? + Gk. –phrenia (“mind”)]

Key: OU = origin unknown