What does "dead giveaway" mean?

A giveaway that is especially obvious, especially ruinous, or both, disclosing, usually unintentionally, a fact or an intention.

Dead giveaway

Common synonyms include: babbling, betrayal, blabbering, blabbing, communication leak, divulgation.

noun

noun ·Rare ·Advanced level

Noun

1
A giveaway that is especially obvious, especially ruinous, or both, disclosing, usually unintentionally, a fact or an intention. idiomatic
"That disguise is a dead giveaway! Choose something less obvious."

"That disguise is a dead giveaway! Choose something less obvious."