An Etymological Dictionary of the German Language/Frosch
Frosch, m., ‘frog,’ from the equiv. MidHG. vrosch, OHG. frosk, m.; corresponding to Du. vorsch, AS. forsc (E. dial. frosk), OIc. froskr, ‘from’; Goth. *frusqa- is by chance not recorded. Before the deriv. sk a guttural has dropped out, as is seen in the cognate terms. AS. frogga, E. frog, would be in Goth. *frugga (*frugwa?); also akin to AS. frocca, earlier E. dial. frock, as well as OIc. fraukr, ‘frog’ (so too MidE. frûte, froute, ‘toad’). Goth. *frusqa-, for *fruhsqa-, therefore be connected with a root ending in a guttural; perhaps the pre-Teut. root pruk?. Hence the attempts to connect the word with frisch or frieren, to which the meaning is also opposed, must be rejected.