We are developing a new data repository to support data-driven developments in materials science, and it became necessary to build an open vocabulary set to describe metadata such as chemical substances, characterization methods, instruments, units, etc. There have been efforts to build a standard vocabulary or an ontology for materials science, but what should be considered as the essential concepts and how to structure them can be quite domain-specific, varying from one researcher to another, as materials science is an interdisciplinary field that encompasses chemistry, physics, and biology. To address this, we are developing a wiki-powered vocabulary management service, not only to apply aforementioned earlier efforts, but also to allow building on top of them by 'crowd-sourcing' among the researchers, thereby realizing appropriate metadata description for a highly-usable materials data repository.