"instrument by which a ship is steered," from Old English helma "rudder; position of guidance, control," from Proto-Germanic *helmaz (source also of Old Norse hjalm, Old High German helmo, German Helm "handle"), from PIE *kelp- "to hold, grasp" (see helve).
Helm - the handle or tiller, in large ships the wheel, by which the runner is managed; the word is sometimes used with reference to the whole stearing [sic]-gear.
Rudder - that part of the helm which consists of a broad piece of timber, enters the water, and is governed by means of the wheel or tiller.
Tiller - the bar or lever by means of which the rudder of a ship or boat is turned.
[J.H.A. Günther, "English Synonyms Explained & Illustrated," Groningen, 1904]
"a helmet, a defensive cover for the head," from Old English helm "protection, covering; crown, helmet," from Proto-Germanic *helmaz "protective covering" (Cognates: Old Frisian, Old Saxon, Old High German helm, German Helm, Old Norse hjalmr, Gothic hilms), from PIE root *kel- (1) "to cover, conceal, save." Italian elmo, Spanish yelmo are from Germanic.