EXCHANGE OF KIN AS SECURITY
—“Uncle Curt, what was it called when Kings would exchange Princes for a required amount of time, and keep as their ward the exchanged Prince? As this was keep the Peace.”—
Meaning changes over time. So that’s why it doesn’t immediately come to you.
Hostage: “a lodger held by a landlord as security”.
It’s hostage, although it means something more like ‘guest held as security’. The modern meaning has been twisted – and fairly recently.
COMPARISONS
A hostage held as security under guarantee of safety vs a hostage hold for ransom under threat of harm. So it’s held as hostage (safe), vs held for ransom (harm).
ETYMOLOGY
hostage (n.)
late 13c., from Old French ostage, hostage “kindness, hospitality; residence, dwelling; rent, tribute; compensation; guarantee, pledge, bail; person given as security or hostage” (11c., Modern French ôtage), which is of uncertain origin. Either from hoste “guest” (see host (n.1)) via notion of “a lodger held by a landlord as security” [Watkins, Barnhart]; or else from Late Latin obsidanus “condition of being held as security,” from obses “hostage,” from ob- “before” + base of sedere “to sit,” with spelling influenced by Latin hostis. [OED, Century Dictionary]