Recent studies have explored English vocabulary learning in environments where students used mobile technologies for prescribed vocabulary learning tasks, or tested designed personalized learning systems to enhance student vocabulary learning for short periods of time in language related courses. Dictionary use via mobile devices has mostly been used for referential purposes. Referential use refers to applications that provide student access to content such as dictionaries, e-books, etc. at places where learning activities occur, taking advantage of the portability and mobility of mobile devices. Research on free student use of mobile devices to foster incidental vocabulary learning in non-English courses remains scant, and no in-depth studies have been carried out to investigate the value of dictionary use on mobile devices for incidental vocabulary learning in higher education. This one-year multiple-case study investigated undergraduate students' dictionary and other uses of Personal Digital Assistants (PDAs) to enhance their incidental vocabulary learning in an English as a Medium of Instruction (EMI) university. The research findings show: (a) the students made various uses of the PDA to improve their vocabulary learning, namely, referential, situated, constructive, reflective, explorative and conversing uses, (b) the students adopted integrated uses of the tools on the PDA and the computer for their incidental vocabulary learning, and (c) the integrated use of the PDA and the computer shaped the vocabulary learning activities and vice versa. These research results indicate that PDAs can be used in more flexible, novel and extended ways for English as a Foreign Language (EFL) vocabulary teaching and learning in higher education, taking student needs and contexts into consideration.