Glossaries of introductory textbooks in psychology, biology, and animal behavior were surveyed to find whether they included the word 'behavior'. In addition to texts, encyclopedias and dictionaries devoted to the study of behavior were also surveyed. Of the 138 tests sampled across all three fields, only 38 (27%) included the term 'behavior' in their glossaries. Of the 15 encyclopedias and dictionaries surveyed, only 5 defined 'behavior'. To assess whether the term 'behavior' has disappeared from textbook glossaries or whether it has usually been absent, we sampled 23 introductory psychology texts written from 1886 to 1958. Only two texts contained glossaries, and the word 'behavior' was defined in both, An informal survey was conducted of students enrolled in introductory classes in psychology, biology, and animal behavior to provide data on the consistency of definitions. Students were asked to "define the word 'behavior'," Analysis indicated the definition was dependent upon the course. We suggest that future introductory textbook authors and editors of psychology-based dictionaries and encyclopedias include 'behavior' in their glossaries.