This work is concerned with the Portuguese prefix co(n)-, understood as a single prefix which, however, can occur in the different forms com, con and co . In the research, the forms studied were extracted from the lexical constructions where they can be recognized, which leads to a better vision of the range of meanings of the prefix in Portuguese. The primary data of the analysis were collected from the Dicionário Houaiss da Língua Portuguesa. In the investigation, we applied a set of operational concepts and analytical procedures of description from Langacker s Cognitive Grammar. It is assumed, therefore, that the phonological structure corresponding to co(N) evokes a given semantic structure arrived at by means of a set of construal operations under the conceptual substract presented by the context in which lexical constructions with the prefix were used. In turn, the construal makes clear that this prefix not only can have different conventional semantic values, in different lexical constructions as well as in different contexts of use, but also that the different senses are mutually related. The recognition of this mutual relationship is possible once we take one of these meanings as prototypical, or primary, from which other meanings derive, especially by conceptual attenuation factors. This approach allowed us to outline a semantic network that permeates conventional semantic values of the prefix, thus converging with GC s theoretical approach based on a network model, in the sense that the various meanings assumed by certain symbolic unity form a web of relationships among themselves.