According to Roldán (2000) most technical terms are neologisms or special terms designed ‘ad hoc’. However, technical terminology is not always innovative in that many new terms can relate to existing words by means of metaphor, metonymy or polysemy. The present paper shows that Spanish civil engineers use metaphor and polysemy quite frequently in their descriptions of railway masonry bridges. The choice of this topic is motivated by the quantitative and qualitative importance of these types of bridges in Spain. The analysis of masonry bridges abounds in metaphors from medicine and psychology. Thus, we come across terms such as síntomas patológicos (pathological symptoms), intervenciones posteriores (later interventions/operations), mecanismo de agotamiento (mechanism of fatigue), or la rótula de un puente (the joint of a bridge).