Lit. 'head of the honour'. The main seat, or head, of the *honour of a lord holding several manors, on which there would have been many fiefs. It was the administrative centre of a widely distributed honour. When first used this term referred to that place within an honour which was considered the most important, such as a monastery which a lord had founded. The fitz-Walters, for example, who possessed Baynard's Castle in London, did not use it as their caput honoris, even though tenants paid for the castle guards. Instead the caput was at Little Dunmow.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.