river in Henan
溱 is a rare kanji that names a specific river in Henan, China. Its standalone meaning is limited to this geographical reference.
溱 combines the water radical 氵 with 秦, which likely provides the sound. The character was created to name a specific river.
The water radical 氵 beside 秦 suggests a river in the region associated with the Qin dynasty. Picture the Qin River flowing through Henan.
For シン, imagine the Qin River shimmering under the sun: shin -> シン, the sound of the water flowing.