shave head as punishment, prune
髠 centers on cutting or removing hair as a punitive or corrective act: shaving the head as punishment, or pruning away excess.
髠 combines 髟 (hair) with 几, which likely contributes a phonetic element. The exact historical development is uncertain, but the character is associated with cutting or removing hair.
The top 髟 represents hair, and the bottom 几 looks like a small table or stool. Imagine a barber's stool where someone sits to have their head shaved as punishment or to get a prune.
For コン, picture a con artist being punished by having their head shaved: con -> コン, and the hair falls onto the stool below.