A euphemism is a word that you use for a potentially offensive word, to make it sound more polite. collateral can be a few things, but the most common one apart from that in collateral damage, is 'property used to secure a loan'. collateral in 'collateral damage' means secondary. So collateral damage is unintended damage other than the intended damage. So: 'little boys room' is a euphemism for a toilet. Sorry sir, we can't give you a loan, as you do not have enough collateral You need to be very accurate with your bombing - we don't want any collateral damage.

"in a few dictionaries" is correct. "a few" and "few" have related but different meanings. "collateral" is an adjective which means connected or related. It's a formal word used in law and finance, in particular, but can be used in any formal context. It also has a meaning in finance as a noun. "collateral damage" is an expression seen most often in the military context to describe damage (including deaths) unintentionally and indirectly caused as a result of a military operation. A "euphemism" is a coded expression which does not clearly express reality. In your case, I imagine that you saw a description of "collateral damage" as a euphemism. Military people may find it difficult to say clearly that their military operation is likely to cause the deaths of innocent people and so they may use the term "collateral damage" to make it sound more acceptable and less horrific.