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 connotationand the lack of stress changed it to un-. "Except could once be used as a synonym for unless, but the words have now drawn entirely apart" [Century Dictionary].
I ask about only one determinant of change:
the negative connotation. 1. How'd it cause 'on' to change, when the negative connotation is wholly spwaned by 'less'?
- To a Middle English layperson, wouldn't prefixing 'less' with 'un' reverse the meaning of 'unless'? As 'less than good = not good', wouldn't
un + less than good
= not + not good