Principles of teacher professional development and digital lexicographical skills for designing in-service training modules

English as a foreign language teachers often use free access online bilingual dictionaries (FAOBD) to plan their lessons but rarely utilize these dictionaries as didactic resources. This paper outlines the design process, and theoretical foundations involved in designing an in-service teacher module, a byproduct of a multiple case study research, aimed at equipping tertiary EFL educators with the necessary conceptual and procedural knowledge to use these digital lexicographical tools. Data collected from a questionnaire, a semi-structured interview, and an online course evaluation form, applied to a sample of four teachers from a Colombian university, revealed scant teacher training and institutional support, limited motivation to use FAOBDs among teachers and students, and a high incidence of look-up errors. These results underscored the need for the training module. Addressing users’ perspectives, teacher training needs, and leadership support is fundamental to optimizing FAOBD use through enhanced lexicographical skills development.