This paper attempts to develop some relatively well-defined notions that may be of use in descriptive semantics and in some areas of cognitive psychology. These notions are intended as explications of certain terms widely used in these fields such as semantic dimension, semantic feature, semantic space, category, conjunctive category, and sememe. The mode of explication is to develop definitions for these terms in an argument similar to a formal axiomatic system, with emphasis on the applicability of terms to empirical data. (CLK)