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1.
THL
Tight, Heavy Lid. To keep quite about a secret or embarrassing event. As referenced in Community (TV show)
Jeff: I need you to keep a tight, heavy lid on the Indian girl story. Tight, heavy lid.

Abed: Cool, THL.
by paki_ow June 26, 2011
 
2.
THL
Twelve Hour Lime- A party that starts late in the afternoon and only ends after 12 hours have elapsed.
Lets THL this weekend!!!
by kalel689 August 10, 2010