Found:

vagueness

SEMANTICS: the phenomenon that the meaning of an expression is not exactly determined, due to the impreciseness of natural language. In John is tall, the meaning of the adjective tall is vague in the sense that the precise degree of tallness is indeterminable. Vagueness is not to be confused with ambiguity, even though the two are not always clearly distinguishable.

LIT.	Chierchia and McConnell-Ginet (1990)