Uncle Sid is another word for acid/lsd. This is a bitter known slang term, so feel free to say it in public places or infront of relatives without worry!
by savannah!! March 11, 2007
Get the uncle sidmug. by Shane Cline January 16, 2004
Get the Uncle Sidmug. by redgoodness July 8, 2010
Get the Uncle Sidmug.