Anything treasonous involves a betrayal, particularly of your country. Your sister might consider it treasonous if you tell your parents she skipped school to go to the beach.

When we betray our friends or families, that's personally treasonous. To betray your country is legally treasonous, since it's a punishable crime. It would be treasonous for a CIA agent to hand over U.S. secrets to an enemy spy—and the root of treasonous is the Latin verb tradere, "to hand over or betray."

Definitions of treasonous
  1. adjective
    having the character of, or characteristic of, a traitor
    synonyms: faithless, traitorous, treasonable, unfaithful
    deserting your allegiance or duty to leader or cause or principle
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