We investigated the role of 'seriousness' - the moral weight of dishonest acts – as a relevant underlying dimension which can influence associations with key predictors Honesty-Humility and descriptive social norms in higher education. Specifically, we aimed to demonstrate that Honesty-Humility has a stronger negative association with behaviors perceived as more serious, whereas descriptive social norms show a stronger positive association with less serious behaviors. This was assessed in a sample of 856 university students who completed two anonymous surveys at the beginning and the end of a university semester in a nation-wide study. Using multiple methodologies (i.e., cross-validation with independent sample, multi-dimensional scaling, cross-validation with judgements of perceived seriousness by independent raters), we found that seriousness of dishonest behaviors can be consistently and validly measured with observed prevalence. This approach to the measurement of seriousness is especially valuable as it does not require additional effort by the researcher. As predicted, structural equation modeling showed that Honesty-Humility was more strongly associated with serious behaviors, while descriptive social norms were more strongly associated with non-serious behaviors. Taken together, our findings underscore the theoretical significance of seriousness in its role as a key underlying dimension of the academic dishonesty construct. We also offer practical insights based on these findings for the development of more targeted prevention efforts.