One idiom that's been confusing me for some days is 'to say nothing of'. The Free Dictionary gives entries such as 'not to mention someone or something' and 'not even considering or mentioning the full significance of something or someone'. I'm not sure what the general meaning of the idiom is. Does it mean 'in addition to the subject being mentioned' or does it mean 'this subject fails to provide sufficient context to make the overall meaning clear'?
Here's another definition and example sentence I've looked up on Wiktionary.org:
"to say nothing of
Definition: (idiomatic) An apophasis used to mention another important, usually related, point: not taking into account, not to mention, without considering.
Example: She had already eaten a large lunch, to say nothing of a full cooked breakfast that morning"
I'm still confused about this idiom's meaning.