KJV Dictionary Definition: lest
LEST, con. That not; for fear that.
Ye shall not eat of it, neither shall ye touch it, lest ye die. Gen. 3.
The phrase may be thus explained. Ye shall not touch it; that separated or dismissed, ye die. That here refers to the preceding command or sentence; that being removed or not observed, the fact being not so, ye will die.
Sin no more, lest a worse thing come to thee. John 5.
Sin no more; that fact not taking place, a worse thing will happen to thee.