Competency with mathematics requires use of numerals and symbols as well as an understanding and use of mathematics vocabulary (e.g., "add," "more," "triangle"). Currently, no measures exist in which the primary function is to gauge mathematics-vocabulary understanding. We created a 64-item mathematics-vocabulary measure for first grade and piloted the assessment with 104 first-grade students. We also administered standardized measures of general word knowledge and mathematics fluency to investigate the validity of the mathematics-vocabulary measure. Results indicated a wide variability in how first-grade students interpret mathematics-vocabulary terms but strong reliability for the mathematics-vocabulary measure.