LET.In Anglo-Saxon lætan meant to permit and lettan, to hinder. In course of time both words were spelled let. Consequently in AV [Note: Authorized Version.] , besides its modern meaning of permit, the vb. let sometimes has the opposite meaning of hinder. Thus 2Th_2:7, only he who now letteth will let, until he be taken out of the way. The other places are Exo_5:4, Num_22:16 m, Isa_43:13, Wis_7:22, Rom_1:13.
Hastings' Dictionary of the Bible
Edited by James Hastings, D.D. Published in 1909
(κατέχω, katéchō): Usually in the sense of ?permit? (Anglo-Saxon, leatan), but also in Old English with meaning of ?hinder? (Anglo-Saxon, lettan). This latter sense is found in 2Th_2:7 the King James Version, ?Only he who now letteth will let,? where the Revised Version (British and American) has, ?Only there is one that restraineth now.?
International Standard Bible Encyclopedia
PRINTER 1915.