lest, conj. = [OED] Etymology: Old English phrase þý lǽs þe , lit. ‘whereby less’
= Latin quōminus
(þý instrumental of the demonstrative and relative pronoun + lǽs less adj. + þe relative particle). In Middle English the first word of the phrase was dropped,
and les þe became les te in accordance with the general rule that þ after s changed into t.
1.a. [...] = Latin nē, English that..not, for fear that.
[Etymonline] [Similar to Wiktionary's entry]
c. 1200, contracted from Middle English phrase les te "less that,"
from Old English phrase þy læs þe "whereby less that,"
from þy, instrumental case of demonstrative article þæt "that" + læs (see less) + þe "the."
The þy was dropped and the remaining two words contracted into leste.
How should the etymology be interpreted, to understand how "less that"
evolved and drifted semantically to mean:
OED's definition 1a above (that..not, for fear that)?
What semantic drifts connect "less that" with that..not, for fear that?