An Etymological Dictionary of the German Language/Linse
Linse, f., ‘lentil, lens,’ from the equiv. MidHG. linse, OHG. linsi, f., with the MidHG. and OHG. variant linsîn. It is not certain whether the word comes from Lat. lens, f., because other borrowed terms are based not on the nomin. of the Lat. word (comp. Kreuz, Kelch, yet also Pabst), but on the stem appearing in the oblique cases; hence Lat. lent- (as is shown by AS. lens) ought to have appeared as *linz- in HG. An analogous case of an apparent permutation of nt to ns is furnished by E. flint, equiv. to OHG. flins, MidHG. vlins (see Flinte); these difficulties are not yet solved. Erbse, however, testifies that we are not compelled to assume that Linse was borrowed from Lat. Comp. also OSlov. lęšta (from *lentja), Lith. lènszis, ‘lentil.’