Expressive writing can enhance cognitive processing and improve stress regulation. Particularly, the use of cognitive words (i.e., insightful and causal words) in writing may be associated with the process of meaning making and promotion of post-traumatic growth (PTG). The aim of the present study was to determine how expressive writing and the use of causal and insightful cognitive words influenced meaning making and PTG during writing. In total, 52 traumatized university students were recruited and randomly assigned to one of two writing conditions involving either an expressive writing task or a neutral writing task. The results showed that participants who engaged in expressive (vs. neutral) writing showed higher scores on the presence of meaning and PTG in the post-writing, self-report questionnaires. Moreover, writing task (expressive or neutral) and frequency of causal and insightful cognitive words were both significant predictors of meaning, which in turn led to high levels of PTG. In conclusion, the use of causal and insightful words might be a fundamental cognitive process for developing meaning in writing, which is essential for our further understanding of meaning making and PTG.