This paper discusses the form of entries and definitions in specialized dictionaries (e.g.,
dictionaries of the sciences). It is proposed that specialized dictionaries in the form of an Explanatory Combinatorial Dictionary avoid the problems of vagueness that afflict other specialized dictionaries. Some sample ECD entries for terms from geology, zoology, and physics are given. The paper closes with a discussion of the implications of specialized ECD's for such things as on-line dictionaries and translation.