Zounds!For info, https://www.oed.com/information/editorial-policy/how-words-enter-the-oed/?tl=true
The OED maintains a higher standard than the Cambridge Dictionary, but still adds words from all manner of sources every year. It has to, in order to preserve English as a living language rather than a dead one.
- which is in the OED: https://www.oed.com/dictionary/zounds_int?tl=true and was probably considered slang when it first appeared in the 1500's.