perfidious vs treacherous

perfidious and treacherous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
perfidious	No	Yes	No	No
treacherous	No	Yes	No	No

As adjectives, perfidious and treacherous are synonyms defined as:

perfidious and treacherous: tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans

Other synonyms of perfidious include punic.

perfidious (adjective)	treacherous (adjective)
tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans	dangerously unstable and unpredictable
	tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans