to permit, is the Anglo-Saxon læt-an, to suffer or permit; but let (to hinder) is the verb lett-an. It is a pity we have dropped the second t in the latter word.
“Oftentimes I purposed to come unto you, but was [have been] let hitherto.” - Romans i. 18.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894