Collateral damage

Collateral damage is a military euphemism that was made popular at the time of Vietnam War (Army Technology). The euphemism has now been in use so long that it is an accepted term within military forces, meaning "unintentional damage or incidental damage affecting facilities, equipment or personnel, happening as a result of military actions directed against targeted enemy forces or facilities. Such damage can occur to friendly, neutral, and even enemy forces."

Etymologically, the expression "collateral damage" probably was originally used as military doublespeak rather than a euphemism, as the adjective "collateral" doesn't seem to have been used as a synonym for "unintentional" or "accidental" earlier. However, "collateral" may also sometimes mean "additional but subordinate," i.e. "secondary", and that specific meaning of a rather obscure word in the English language seems to have been picked up and broadened by the military in the expression "collateral damage."