Английский Этимологический словарь - let (v.)

- O.E. lжtan "to allow, let go," also "to rent" (class VII strong verb; past tense let, pp. lжten), from P.Gmc. *lжtan. The primary sense appears to be "to let go through weariness, to neglect." Obsolete let (n.) "hindrance" is from O.E. lettan "hinder, delay," from P.Gmc. *latjanan, related to Mod.Eng. late. Slang letdown "disappointment" first recorded 1889.