I believe expressions in this case means words that refer to the concept, they are however wrong because I will be thinking about it in a fortnight.
One thing I found mildly interesting about the distinction between English and Spanish is that English has "tonight" but no single word for "last night", whereas in Spanish it's the opposite.
probably not understandable to many English speakers - however archaisms might not be equally archaic in every region and dialect of English.