letter_bomb
1. [ verb ] (military) send an explosive to
Examples:

"The Unabomber letterbombed a number of individuals and institutions"

Related terms: bombard
2. [ noun ] (military,arms) a thin explosive device inside an envelope or package and detonated when opened
Synonyms: parcel_bomb package_bomb
Related terms: bomb
Similar spelling:   letter-bomb
  letter_box
  letter_bond
  letter_paper
  letter_opener