An Etymological Dictionary of the German Language/Laster
Laster, n., ‘vice, crime,’ from MidHG. and MidLG. laster, n., ‘abuse, disgrace, mistake,’ OHG. lastar, n. It is connected with a str. vb. lahan (for the loss of h before s comp. Mist) preserved in OHG., equiv. to AS. leán, ‘to blame.’ Pre-Teut. lahstra- is formed from the verbal stem lah with the suffix stra-, which represents the earlier form tra seen in AS. leahtor, n., ‘reproach, sin’ (obsolete in E.). Another derivative from the same stem is seen in Scand. lǫstr (Goth. *lahstus), MidE. last, ‘mistake, defect.’ In the non-Teut. languages the word may be compared with OIr. locht (from lokto-), ‘mistake.’