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1.
A step mother who is vicious and mean.
My step monster wont let me do what I want.
by Sandi68 April 13, 2006
 
2.
The word used to identify a stepmother that you don't like, get along with, just plain despise. 1st coined in the film St. Elmo's Fire, used chiefly by Demi Moore's character, Jules.
Jules: I have to go. Did the hospital call? Did my stepmonster die?
by Tommyt July 29, 2008
 
3.
A step mother who is a nightmare to the other children. Known to fight for the mother title in many sinister ways. Pouts when the real mother is in contact with the child or grandchildren. Has no concern about how that looks to anyone..kids, grandkids. A total "one-upper" in every breath
Dammit, my stepmonster Lisa wont leave my mother alone. I mean who do she thinks she is, she has never been and will never be a mother to me
by llp1964 April 03, 2009