Ampfer.

From the equivalent Middle High German ampfer, Old High German ampfaro m, allied to the equivalent Old English ompre, from Proto-West Germanic *amprō; an adjective used as a substantive. Compare Dutch amper (“sharp, bitter, unripe”), Old Swedish amper, Old Norse apr (“sharp, chiefly of cold”) (for Proto-Germanic *ampraz); also Low German ampern (“to prove bitter to the taste”). Sauerampfer (also corrupted to Sauer-ramf) is a tautological compound like Windhund. In case *ampraz, from earlier Pre-Germanic *ambras, represents the properly Proto-Indo-European *amrós (see *h₂eh₃mós), Sanskrit अम्ल (amlá, “sour; wood-sorrel”) and Latin amārus (“bitter”) are primitively cognate with this word.