This paper examines the use and role of the term "hypothesis" in science teacher education as described by teacher students. Data were collected through focus group interviews conducted at seven occasions with 32 students from six well-known Swedish universities. The theoretical framework is a sociocultural and pragmatist perspective on language and learning, introducing the notion of pivot terms to operationalise language use as a habit and mediated action. We describe three different customs of using the term "hypothesis" within four cultural institutions that can be said to constitute science teacher education in Sweden. Students were found to habitually use the term hypothesis as meaning a guess about an outcome. This is contrasted to the function of this term in scientific research as a tentative explanation. We also found differences in how this term was used between the pure science courses given by the science departments of universities and science education courses taken only by teacher students. Findings also included further support for school students hypothesis fear reported in an earlier study. It is discussed how these findings can obstruct learning and teaching about the nature of scientific inquiry. Constructivist theories of learning are suggested as a possible origin of these problems. The findings are also related to curricular reform and development. (Contains 1 table.)