A small castle or castle-like structure; a diminutive version of a castle.
From castle with the diminutive suffix -let (from Old French, meaning 'small'). This suffix appears in English words like booklet, tablet, and droplet.
The suffix -let is how English makes 'cute' or 'small' versions of things—castlet was one way medieval people described small fortified houses that weren't quite full castles but still had defensive features.
Complete word intelligence in one call. Free tier — 50 lookups/day.