What underlying notions explain this same semantic shift from 'less' to 'not' (ie: negation)? It appears in all 4 languages below, as evidenced by the Spanish and Portuguese synonymy.
I know that in English, 'less than' can euphemise 'not'. E.g, from Hamlet, Act 1, Scene 2, Page 3, Scene 5, Line 65:, in uttering (as an aside) that Claudius is 'less than kind', Hamlet really means Claudius is NOT 'generous' (and that Hamlet is not really Claudius's child, because Shakespeare was punning bilingually with English and German). But are there any other explanations?
The etymology for 'unless' reveals the etymon of 'un' as 'on', which then suggests 'un ← on' to mean the same as à and a.
mid-15c., earlier onlesse, from (not) on lesse (than) "(not) on a less compelling condition (than);" see less. The first syllable originally on, but the negative connotation and the lack of stress changed it to un-. "
à moins que = sauf si.