An Etymological Dictionary of the German Language/Annotated/Helm
Helm (1.), masculine, ‘helmet,’ from the equivalent Middle High German and Old High German hëlm, masculine; the same in Old Saxon, Old Frisian, and Anglo-Saxon (Anglo-Saxon hëlm, ‘helmet, protector,’ English helm), Old Icelandic hjalmr, Gothic hilms, ‘helmet’; a common Teutonic strong noun, helma-, ‘helmet,’ from pre-Teutonic kelmo-. Compare Old Indian çárman-, neuter, ‘protection’ (compare the Anglo-Saxon meaning), with which the root kel in Modern High German hehlen, hüllen, is connected. Lithuanian szálmas, ‘helmet,’ and Old Slovenian šlěmŭ, ‘helmet,’ were borrowed at an early period from Teutonic; so too the Romance class — Italian elmo (French heaume), ‘helmet.’
Helm (2.), masculine ‘tiller,’ Modern High German simply, from Low German, whence a number of nautical terms found their way into High German (see Boot, Kahn, Barke, Flagge, Spriet); compare Dutch helmstock, ‘tiller.’ English helm, Anglo-Saxon helma, ‘rudder,’ Scandinavian hjálm, feminine, ‘tiller.’ In this case, as in most of the other nautical expressions, it cannot be decided in which division of the Saxon and Scandinavian group the technical term originated; as in other instances — see Boot, Bord — Anglo-Saxon contains the earliest record of the word. The Middle High German helm (see Hellebarte), ‘helve, handle,’ which occurs only once, and its variant halme, do not seem to be actually allied to the present term; they are connected with Halfter.