An Etymological Dictionary of the German Language/Annotated/Sturm
Sturm, masculine, ‘storm, tumult,’ from Middle High German and Old High German sturm, masculine, ‘tempest, fight’; compare Dutch storm, Anglo-Saxon and English storm, and the equivalent Old Icelandic stormr. From the common Teutonic storm (sturm) are derived the Romance cognates, Italian stormo, ‘concourse, encounter, quarrel,’ which proves the primitive use of the word in the figurative sense of ‘fight’ (English stour is based on the corresponding Old French estour). The Teutonic root stur is a relic of the Aryan root ser (sṛ from stur?), to which Greek ὁρμή, ‘attack, impact,’ Sanscrit root sṛ, ‘to stream, hasten,’ belong (for str from sr, see Schwester and Strom). Others prefer to regard the word as primitively cognate with Latin sternere, ‘to throw down.’