Castle – A large fortified building.
The word castle came to English with the French occupation following 1066, and was a variant of the French word ‘castel’ – which has become ‘chateau’ in French today. ‘Castel’ came from the Latin word ‘castellum’ meaning ‘fortified village’ – the Romans preferring to create villages as strongholds rather than single buildings. When the Roman empire collapsed and fell back from most of Europe, defence shifted to hill forts rather than well-defended villages and the term ‘castellum’ was applied to these too.
‘Castellum’ has its roots in the Proto-Indo-European language where the word was ‘kastro’, which meant ‘share’. It’s easy to see how this could refer to a village as it would be a way to share resources and labour.