Metonymic cognition as well as its linguistic representation is a hot topic in contemporary cognitive linguistics. Existing research has supplied ample discussion of all sorts of contiguity relations underlying metonymic cognition and systematic description of corresponding linguistic representation and speech act realization, and revealed the motivation and effects of metonymy use. The present study addresses an under-explored type of metonymy, i.e. metonymy realized by adjective opposites with regard to its cognitive foundation, cognitive mode and features, and metaphorization. It will be argued that the part-whole relation based on opposition gives rise to the metonymic usage of adjective opposites, and the derived metonymic usages may undergo both conceptual and grammatical metaphorization. Specifically, metonymies represented by adjective opposites involve either the substitution of the whole of an object for part of it (or the other way round), or that of a property of the object for the object itself; thus, they are cognitively motivated. Yet, in actual communication, the emergence of such metonymies depends on the context at the moment. Unless a part or a property of the object becomes salient in the current discourse, can it be used to refer to the whole object, or be substituted by the object. In addition, since shape and property stand for different aspects of an object from process and result, the differences in the focus with which the cognizers perceive them will yield different cognitive results, giving rise to nominalization or other grammatical-metaphoric processes. The metonymization as well as subsequent conceptual and grammatical metaphorization of the adjective opposites is not unique to Chinese language or cognition, but the combinational power of its compounding does facilitate the processes. This study will shed light on the cognitive mechanism of the metonymic usages of the opposites and provide implications for the teaching of adjective opposites.