The condition of a sign which has an empty, absent, non-existent, paradoxical, hypothetical, supernatural, or undefined referent, such as nothing, null, vacuum, or void
An assumed zero value of a quantity relative to which magnitudes of the quality are measured, or a structure having this zero value of the quantity; e g , a voltage measured relative to the ground as a referent
something that refers; a term that refers to another term the first term in a proposition; the term to which other terms relate something referred to; the object of a reference