English Idioms and Phrases: Armed to the Teeth
To be armed to the teeth means to be heavily armed, in other words someone or something who is carrying a lot of weapons
"It's too dangerous to attack that tank, it is armed to the teeth"
or "Don't go out into the city unless you're armed to the teeth"
Port Royal in Jamaica was famous for piracy in the 17th century and this is where this phrase originates from.
The guns that these pirates carried only held a single shot meaning that many of them would carry several pistols and cutlasses so that they could continue the fight.
As well as the many pistols and cutlasses they would often be seen carrying a knife in their mouth, clenched in their teeth. Aside from this, when swimming, in the teeth was the easiest way to carry the knife. Thus these men were armed to the teeth.
Alternatives or Synonyms
Armed, well-armed, heavily armed, equipped