Yunnan province
滇 is a proper noun referring to Yunnan province in China. It has no common standalone meaning beyond this geographic name.
滇 combines 氵 (water) with 真, likely as a phono-semantic compound used for the name of a lake or region in ancient China. The exact historical development is uncertain.
The water radical 氵 beside 真 suggests a place name tied to a body of water. Picture a true (真) lake (氵) in Yunnan province.
For テン, imagine ten (テン) true (真) lakes (氵) scattered across Yunnan: ten -> テン.