チン, ジン, しず.む, しず.める, しん
sink, be submerged, subside, be depressed, aloes
JLPT2 G7 S7 F1271
The relevant oracle bone form of 冘 shows that it originally combined 川 river and 牛 cow → drive cattle across a river, their bodies sinking in being largely submerged. A bronzeware inscription form alters the character by showing a person weighed down by a heavy bar across the shoulders → slump; sink. 沈 is 冘# + 水 water → sinking person/object (compare 没) → *sink*; *immerse*; *submerge* → *go down*; *set*; *be mired in*.
[Full Kanji Etymology List]