The word "perfidiou" is typically used to describe someone who is deceitful, treacherous, or untrustworthy. Synonyms for the word include terms such as dishonest, traitorous, duplicitous, and unreliable. Other related words that could be used interchangeably with "perfidiou" include phrases like disloyal, faithless, false, or insincere. Depending on the context in which the word is being used, synonyms may vary slightly in their meaning or connotation, but all of these terms carry an implication of betraying trust or acting with malice towards others.