designatum vs referent

designatum and referent both are nouns.

Word	Noun	Adjective	Verb	Adverb
designatum	Yes	No	No	No
referent	Yes	Yes	No	No

As nouns, referent is a hypernym of designatum; that is, referent is a word with a broader meaning than designatum:

designatum: something (whether existing or not) that is referred to by a linguistic expression
referent: something referred to; the object of a reference

designatum (noun)	referent (noun)
something (whether existing or not) that is referred to by a linguistic expression	something referred to; the object of a reference
	the first term in a proposition; the term to which other terms relate
	something that refers; a term that refers to another term

designatum (adjective)	referent (adjective)
	having reference