It generally falls under semiotics, a subdivision of linguistics. I don’t know of any idea that includes part 2 - all “thing-names” are nouns.
Saussure defined a three-stage model of signifier, signified and referent. Those are (sort of) 1, 3 and 4 respectively, or maybe 3, 1, 4 depending on what you mean…
Signifier is the word itself, the sequence of sounds and letters.
Signified is the concept that the word is attached to in a language.
Referent (if applicable) is the actual object to which the concept refers.