Mulct is a very strange word to say. Go on, say it out loud a couple of times. Mulct. Mulll-ktt. Bleh. In this case, it's an unpleasant sounding word for an unpleasant concept!
Mulct is a verb which can mean: to punish by a fine, to swindle someone, or to obtain something [usually money] by fraud, duress, or theft.
A particularly unfair instance that comes to mind is an overdraft fee. Why am I being punished for not having enough money by owing additional people money? In that instance I am mulcted in what I feel are both uses of the word– both as in being fined and as in the sense of suffering pure theft at the hands of the bank!
I hope you have no cause to actively use this word, but if you do, make sure you spit it out with enough derision so that the person doing the mulcting feels bad.
–C