From Latin 'castellum' (small fort), from 'castrum' (camp) — same root in every '-chester' and '-caster' place name.
A large fortified building or group of buildings with thick walls, typically of the medieval period.
From Old English 'castel' (village, town), borrowed from Late Latin 'castellum' (fort, fortified place), a diminutive of 'castrum' (fort, military camp), from PIE *kat- (to braid, to weave) — referring originally to a wattled or woven fortification. The meaning shifted from 'any fortified settlement' to specifically 'a lordly stronghold' after the Norman Conquest, when the Normans built castles across England as instruments of control. Key roots: castrum (Latin