"treacherously" is correct and usable in written English.
It is an adverb often used to describe an act that has been done in a malicious and deceptive way. Example sentence: He betrayed me treacherously, without a hint of remorse.
Russia claims that Mr Saakashvili treacherously broke a unilateral ceasefire he had just announced, ordering a massive offensive on Tskhinvali, ethnically cleansing South Ossetian villages and killing as many as 2,000 people.
"I thought that the authorities can and should behave more subtly, smarter, and with cunning," he said".But it turned out that they behave roughly, treacherously, and recklessly, without concealing or masking their actions".
He leaked the result of an opinion poll to the Guardian, which he had himself treacherously commissioned, which suggests that the Lib Dems are heading for another wipe-out at next year's general election.
Anonymous American officials leaked news that Israel has been treacherously spying on them during the Iran talks and briefing Congress a charge Israel denies.
Mr Klaus's office was also one of the first to condemn the speech, as one of the president's deputies said the speech "is a basis for which, combined with the Lisbon Treaty and the treacherously non-ratified Klaus opt-out, makes the door wide open for property claims raised by deported Germans".
Imposing a punitive tax on the defeated might possibly be legitimate, for a time, in the aftermath of a defensive war; but a war could only be considered "defensive" and permissible if the adversary behaved treacherously, for example by breaking a treaty.
The governor of New Jersey, Chris Christie (knowing that many at CPAC think him a treacherously squishy centrist) biffed and bashed Mr Obama and raised cheers when he bellowed: "We have to stop letting the media define who we are and what we stand for .Yet at the same time speakers earned applause for warning that America was in dire straits.
If they answer with any certainty it's a bluff: exchange rates are treacherously difficult to predict.
This will be the first involving the Mets formed in 1962 filling a gap left when the Dodgers (as well as the New York Giants) treacherously went west.Rivalry between Mets and Yankees fans has traditionally been intense but friendly.
Romanus was treacherously blinded.
Aristotle helped Hermias to negotiate an alliance with Macedonia, which angered the Persian king, who had Hermias treacherously arrested and put to death about 341.
