look up any word, like blumpkin:
A term to describe a bet that is virtually guaranteed winner, but in reality it is just a coin flip.

The term is a modification of the term, lock, which is used to describe a guaranteed winner in sports betting.

The use of this term is introduced by a poster, Richkas, who use the term to gain attention for his sports gambling picks. Due to the fact that his mortal locks are no better than a coin flip, the term is usually used as a comical modifier for sports gambling picks.

There are several variations of the term lock. Some popular variations are, Sicilian Lock, bet your mother's house lock, and $$$mortal lock$$$.

St. Louis Cardinals is a mortal lock.

Bet the blues, it is a mortal lock.
by picoman March 31, 2009
Something that cannot lose. 100% sure bet.
Michael Schumacher to win the WDC is a Mortal Lock!
by Riker! July 24, 2006