well, there are certainly adjectives which cover the concept. a word can be monosemous (as opposed to polysemous) or it can be univocal (as opposed to equivocal); come to think of it, I believe univocal is also used as a noun....

...I see the noun form of the former is monosemy, having a single meaning (absence of ambiguity) usually of individual words or phrases [dictionary.com]