An Etymological Dictionary of the German Language/Rätsel
Rätsel, n., ‘riddle, perplexity,’ from the equiv. MidHG. râtsal, rœtsel, n., OHG. *râtisal, n.; comp. OLG. râdisli, MidLG. rêdelse, Du. raadsel, AS. rœ̂dels (for *rœ̂desl), m., whence the equiv. E. riddle, the s of the AS. word being regarded as a sign of the plur. The formation of the subst. from raten corresponds to that of Mühsal from mühen, of Labsal from laben, and of Trübsal from trüben. The notion ‘riddle’ was current among the Teutons from early times; the Goth. term was frisahts; in OHG. we find tuncal, n., and râtussa, râtissa, f. ‘riddle.’