Note 2 — Chapter IV · DEGENERACY OF WORDS.
Reading edition
In some cases, this difference of meaning may be accounted for by a difference of etymology. ‘To let,’ in the sense of ‘to hinder,’ is from the Saxon verb ‘letjan;’ but when it means ‘to allow,’ it is from the Saxon ‘lætan.’ See Mätzner, Englische Grammatik, vol. i. p. 189.