letter-bomb

from The Collaborative International Dictionary of English v.0.48

letter bomb \let"ter bomb`\, letter-bomb \let"ter-bomb`\n.
   A bomb disguised as a letter and sent through the mail,
   usually rigged to explode and kill or harm the recipient when
   opened.
   [WordNet 1.5]

from The Collaborative International Dictionary of English v.0.48

letter-bomb \letter-bomb\ v. t.
   to send a letter-bomb to.
   [WordNet 1.5]