схованка, схов, сховок, тайник, потайник
dead drop / dead-drop exchange
letter bomb (parcel bomb, mail bomb, postal bomb etc)
letter of instruction
letter order
letter of agreement
letter of commendation
action letter
immediate action letter
call letter
speed letter
recruitment letter
command letter
circumstantial letter
commendatory letter
Mike (letter M in the phonetic alphabet)
Air Force letter
personnel news letter
letter of censure
dead mine
dead space
land dead on target
top dead center (TDC)
dead ahead
dead eye
dead radio
dead hand
dead load
dead mileage
dead stop
dead zone
dead-center ignition
dead-end road