This study explored the behaviour and functions of term variation in research articles in order to better understand the process of knowledge construction within texts. A semantic analysis of term variation in 19 Spanish-language psychology research articles was carried out. Variants were classified according to the semantic distance from the base term. Analysis revealed that term variation provides information about the concept’s content and its relationships with other concepts within the conceptual structure. Furthermore, an examination of the distribution of term variants across text sections revealed three rhetorical functions of term variation: a naming function, present in the title, abstract and keyword sections; an explanatory function, in the introduction and discussion sections; and a particularizing function, in the method and results sections. This analysis confirmed that intratextual term variation plays a cognitive and rhetorical function in research articles, helping to construct and transfer knowledge within the text and to realize the communicative purposes of the genre.