Definition of "homonym"

(semantics, strict sense) A word that both sounds and is spelled the same as another word.  examples

(loosely) A word that sounds or is spelled the same as another word (but not necessarily both), technically called a homophone (same sound, different spelling) or a homograph (same spelling, different sound), or if both are the same, a homonym.  examples

(taxonomy) A name for a taxon that is identical in spelling to another name that belongs to a different taxon.  examples