prisoner

A person held in custody, captivity, or a condition of forcible restraint, especially while on trial or serving a prison sentence.

One deprived of freedom of expression or action.

(take no prisoners) To kill all of an enemy or a population.

(take no prisoners) To be ruthless or unrestrained, as in an undertaking.

In mech., a piece of metal used to connect two adjacent parts of the rim of a fly-wheel. The prisoner is usually put in place in recesses in the rim while hot, so that its contraction during cooling will draw the two parts of the rim together very tightly.