rudder vs steering mechanism

rudder and steering mechanism both are nouns.

Word	Noun	Adjective	Verb	Adverb
rudder	Yes	No	No	No
steering mechanism	Yes	No	No	No

As nouns, steering mechanism is a hypernym of rudder; that is, steering mechanism is a word with a broader meaning than rudder:

rudder: (nautical) steering mechanism consisting of a hinged vertical plate mounted at the stern of a vessel
steering mechanism: a mechanism by which something is steered (especially a motor vehicle)

Other hypernyms of rudder include steering system.

rudder (noun)	steering mechanism (noun)
(nautical) steering mechanism consisting of a hinged vertical plate mounted at the stern of a vessel	a mechanism by which something is steered (especially a motor vehicle)
a hinged vertical airfoil mounted at the tail of an aircraft and used to make horizontal course changes