Learner's definition of PRISONER
1 : a person who is kept in a prison 2 : a person who has been captured and is being kept somewhere
— sometimes used figuratively
He was captured by rebel forces and kept as their prisoner for several months before they set him free.
They took him prisoner. = He was taken prisoner. [=they captured him and made him their prisoner]
The families were held/kept prisoner for four days.
take no prisoners
: to deal with the people you are competing with or trying to defeat in a very harsh way without mercy