Dead Giveaway

An incontrovertible sign that something is the case, that it is true.
"There were many things that pointed to murder, but the dead giveaway was when they found the bloody knife buried in a freshly dug hole in the backyard."

"Her failure to disclose her relation with the victim was a dead giveaway that something was very wrong with her testimony."
by ScorpionWasp December 10, 2015
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