Semantic properties or meaning properties are those aspects of a linguistic unit, such as a morpheme, word, or sentence, that contribute to the meaning of that unit. Basic semantic properties include being meaningful or meaningless – for example, whether a given word is part of a language's lexicon with a generally understood meaning; polysemy, having multiple, typically related, meanings; ambiguity, having meanings which aren't necessarily related; and anomaly, where the elements of a unit are semantically incompatible with each other, although possibly grammatically sound. Beyond the expression itself, there are higher-level semantic relations, that describe the relationship between units: these include synonymy, antonymy, and hyponymy.