Ooh! Did I make a funny?
Another of the dateless, let comes from the Old English laetan, leave behind or allow. Before that, it was the Proto Germanic letan and Proto Indo European le-, to let go. There’s also an older, not used anymore definition of let that means hinder or obstruct. It actually has a different history than the common let, coming from the Old English lettan, delay, and Proto Germanic latjanan, which happens to be an ancestor of the word late. Latjanan does come from le-, though, so the two lets are still somewhat related.
Tony Jebson’s page on the Origins of Old English
University of Texas at Austin Linguistic Research Center