Monosyllabism is the name for the property of single-syllable word form. The natural complement of monosyllabism is polysyllabism.
Whether a language is monosyllabic or not sometimes depends on the definition of "word", which is far from being a settled matter among linguists. For example, Modern Chinese (Mandarin) is ""monosyllabic"" if each written Chinese character is considered a word; which is justified by observing that most characters have proper meaning(s) (even if very generic and ambiguous). However, most entries in a Chinese dictionary are compounds of two or more characters; if those entries are taken as the "words", then Mandarin is not truly monosyllabic, only its morphemes are.
Few known recorded languages preserve simple CV forms which apparently are fully functional roots conveying meaning, i.e. are words--but are not the reductions from earlier complex forms that we find in Mandarin Chinese CV forms, almost always derived with tonal and phonological modifications from Sino-Tibetan *(C)CV(C)(C)/(V) forms.
an overwhelmingly high percentage of Chinese segmental morphemes (bound or free) consist of a single syllable; no more than perhaps five percent are longer than one syllable, and only a small handful are shorter. In this sense -- in the sense of the favored canonical shape of morphemes -- Chinese is indeed monosyllabic