garrison

From Middle English garisoun, garysoun, from Old French garison, guarison, from guarir plus the suffix -ison, ultimately of Germanic origin. It's a doublet of warison, and its modern military sense was shaped by the now-obsolete word garnison.

The word began as a term tied to protection or safekeeping, and later narrowed to mean the troops themselves that provide that protection to a fortified place — a shift nudged along by the obsolete garnison.

It shares deep roots with guard and ward, all pointing back to the same idea of watching over and defending something.