Top definition
Related to methamphetamine, crank, gilly. If you've ever met a hardcore tweaker they'll report seeing monsters and other hallucinations after being up on the drug for days. Some call them the gillymonster.
fuck dude this one time i was up for 5 days straight and the fucking gillymonster was going to fucking get me!
by RC November 03, 2004
Get the mug
Get a gillymonster mug for your Facebook friend James.