An Etymological Dictionary of the German Language/Annotated/lassen

by Friedrich Kluge

lassen, verb, ‘to let, leave,’ from the equivalent Middle High German lâȥen, Old High German lâȥȥan, strong verb; compare Anglo-Saxon lœ̂tan, English to let, Dutch laten, Old Icelandic láta, Gothic lêtan; the pre-Teutonic form of the common Teutonic root lêt, ‘to leave,’ is lêd (with lad as a weaker gradation, compare laß). The only certain cognate in the other Aryan languages is the Latin word lassus, ‘faint, languid,’ quoted under laß; hence ‘to relax, release,’ is probably the primary meaning of the verbal stem. From this, Middle High German lâȥen, both simply and in compounds, evolved the meanings ‘to set free, omit, leave behind,’ &c., as in Modern High German.