Meerrettich.

From Middle High German merretich, from Old High German meriratih; compare Dutch mierik (from Middle Dutch meerrâdic). By surface analysis, Meer (“sea”) + Rettich (“radish”), from the use of Meer to mean “foreign”, as also in Meerkatze, Meerschweinchen. The fact that horseradish is most often eaten in Germany with fish is coincidental, though speakers may make that connection. Alternative etymologies suggest that the first part of the compound is mehr (“more”, here in the sense of “greater, bigger”) or Mähre (“mare, horse”). However, the Old High German spellings clearly support the first-mentioned derivation. Eventually, this compound may go back to a phono-semantic matching of Latin armoracia.