ラク, お.ちる, お.ち, お.とす, おち
fall, drop, come down, village, hamlet
JLPT3 G3 S12 F420
As per 洛# (connect) + 艸 grass/plant → chain of dewdrops falling from a plant → *drop*; *fall* → *omit*; *settle down*. Other extended meanings from "drop" or "fall" include *collapse*; *come off/out*; *die down*; *decline*; *fail* (a test etc.); *be inferior*; *remove*; *trap*; and *trick*. *Mistake* is via "omit," while *punch line* (of a joke) is by extension from "trick".
[Full Kanji Etymology List]