淡
タン, あわ.い
thin, faint, pale, fleeting
JLPT1 G7 S11 F1436
As per
炎
# (consuming blaze) +
水
water → toss water on a consuming blaze, extinguishing it → *slight*; *pale*; *faint*; *light* (← slight remainder of heat/light).
[Full Kanji Etymology List]