laconic

(adj) using or involving the use of a minimum of words   
Veranda was a laconic speaker and knew how to say a lot with a little.

lassitude

(n) a condition of weariness or debility : fatigue. 
 I wasn't necessarily lazy after the hiking trip, I was experiencing lassitude since I'd gone on another hike just the day before.

laud

(v) praise, extol  
 The valedictorian graduated magna cum laude and all of her professors lauded her hard work ethic.

lethargic

(adj) sluggish; indifferent   
Jabba the Hut seemed like a lethargic blob but actually moved quickly given his mass.

levee

(n) a reception usually in honor of a particular person   
The senator hosted a levee in honor of his biggest donor, who also happened to be turning 80.

levity

(n) lightness in humor or disposition   
Although it was a funeral eulogy, it had its moments of levity.

loquacious

(adj) full of excessive talk; garrulous. 
 The girls in the back of the room were loquacious and chatted all day about boys.

lucid

(adj) suffused with light; having full use of one's faculties.   
Grandma is old but her memories of her childhood in Estonia are amazingly lucid.

luminous

(adj) bright   
A luminous streak lit up the sky; astronomers said it was a comet.