1.
let alone; much less; (and) even more so
Literary conjunction used after a milder case to introduce a stronger one. 'If even X is the case, then certainly Y too' — typically marking the second item as a more extreme example of the same point.
Formal conjunction at the start of a sentence. The structure compares two cases: the first is conceded to be already extreme, and the second is presented as obviously more so. Often pairs with なんて, でも, or はずがない at the end.
Register
- Written and formal speech. In casual conversation, まして or ましてや は more common.
- The full ましてや is interchangeable and slightly more emphatic.