The police discovered a 'sleeper cell' [=a small organized group of spies] that had been operating in the city for years.
Our guests will use the 'sleeper sofa'. [=a sofa that folds out to form a bed]
a light 'sleeper' [=someone who does not sleep well and wakes up easily]
(..) it on U.S. soil. Their plan is to incur maximum civilian casualties. Man is capable of as much atrocity as he has imagination. New Freedom has sleeper agents here in the U.S. McCarthy is an idiot, but, unfortunately, that doesn't make him wrong. New Freedom communicates to its agents... (..)2001 A Beautiful Mind