Definition of underworlds:
(n) :
That part of society that is engaged in crime or vice, and particularly those involved in organized crime.
(n) :
(religion or mythology) The world of the dead, located underneath the world of the living; the afterlife.
(n) :
(video games) The portion of a game that is set below ground.
(n) :
Alternative letter-case form of underworld. [(religion or mythology) The world of the dead, located underneath the world of the living; the afterlife.]