Kahan, also called Kahan no retsu (joint surety) means originally a chief retainer who had authority to sign or put seal at carrying out an order of a lord. The word had often been seen since the end of the Sengoku Period (Period of Warring States).
The word Kahan was used in various meanings by the Edo Shogunate, territorial lords, hatamoto and others.
In the Edo Shogunate, roju (senior councillor of the Tokugawa shogunate) was kahan no retsu, but in the beginning those who were qualified to attend Hyojosho (conference chamber) such as kanjo bugyo (commissioner of finance) were also considered as kahan.
Kahan was used as follows in domains.
1. Kahan (or Kabanshu) was used for the same meaning as karo (chief retainer), or as the name of the social standing of a family and kakaku (family status).
2. Kahan was sometimes used as an official title given to qualified people to attend a conference of chief retainers such as Hyojosho (conference chamber). In such a case, position of karo was naturally kahan, so people in lower positions (bugyo [magistrate], yonin [officer handling domestic economy]) were called kahan at the assignment.
3. There was uncommon example in a domain which had more positions of karo than the size of domain that karo qualified as kahan and karo unqualified as kahan were separated.
4. Sometimes, those who were from karo family were regarded as karo kahan when they became professional karo, and those who were from non karo family were regarded as karo without qualification of kahan when they became karo.