This command forces a user to change nicks, and then prevents the user from changing to any other nick. This may be useful to force the disuse of a nickname that is deemed offensive until the user can be properly warned about the offense. This argument takes two commands, the current nick of the user you wish to target, and the nick you want to lock them too. To change the nick of offensiveuser to nick1, you would issue this command:
/nicklock offensiveuser nick1
To allow the user to change nicks again, simply use nickunlock.
Note that this command is similar to, but distinct from sanick and svsnick. This command will prevent all future nick name changes from that user until they reconnect or the nickunlock command is run on their nickname. Sanick will change their nickname, but then allow the user to switch to another nickname.