There are also other theories such as deriving from 'kan' (貫 in Chinese characters meaning penetration) referring to a thing connected by penetrating through a perforated coin in the Edo period, deriving from 'kan' referring to a unit of weight (also described as 貫 in Chinese characters), and so on.
江戸時代に穴あき銭を貫いて一つなぎしたものの「貫」から転じたという説、重さの単位「貫」から転じたという説などがある。