gam·ma-bu·tyr·o·lac·tone 
(găm′ə-by′tə-rə-lăktōn′)
(găm′ə-by′tə-rə-lăktōn′)n. Abbr. GBL
A chemical that has many industrial uses, especially as a solvent. It is a chemical precursor to gamma-hydroxybutyrate and is ingested illegally for its euphoriant and sedative effects.