IPA: /ˈtriːzənəbl/
KK: /ˈtrizənəbl/
Connected to or involving the crime of betraying one's country, especially by aiding an enemy.
The government took action against those who were accused of treasonable activities.
Treasonable → It is formed from "treason" (from Old French *traïson*, meaning betrayal or treachery) and the suffix "-able" (meaning capable of or worthy of). The word "treasonable" means capable of or worthy of being considered treason or betrayal.
Think of 'treason' as betrayal and remember that 'treasonable' describes something that is worthy of being seen as betrayal.