Abarim Publications' online Biblical Greek Dictionary
The verb φιμοω (phimoo) means to muzzle or gag: to bind shut the mouths of animals, to prevent them from eating or biting, and figuratively of people to keep them from speaking.
This verb comes from the unused noun φιμος (phimos), meaning muzzle, whose origin has been declared unknown by the experts, or at least those experts who are unfamiliar with Biblical Aramaic, in which the word פם (pum) occurs as equivalent of the common Hebrew noun פה (peh), meaning mouth, the off-the-shelf synonym of στομα (stoma), the Greek word for mouth.
This Aramaic word for mouth also appears in the name פום בדיתא (pum b'ditha), Pumbedita, or Mouth of the River, the name of a city in Babylon, where exiled Jews had settled and by the 2nd century CE had established a formidable Jewish academy (which helps to explain Matthew's magi; Matthew 2:1). This academy became one of two schools that ultimately produced the Talmud.
Still, this later so brilliant city not always enjoyed the best of reputations. In Chullin 127a, the Talmud reads: "if someone from Neresh kisses you, count your teeth to make sure he didn't steal one. And if someone from Pumbedita accompanies you on a journey, change your inn because he's probably trying to rob you." That too might explain the existence of our verb φιμοω (phimoo).
Our verb is used 8 times in the New Testament; see full concordance.