1. the co-occurrence of two or more phenomena, especially such that the phenomena are essentially different manifestations of a single underlying reality. For example, a symbol and its meaning may be concomitant. According to Jungian psychology, synchronous events may be concomitant in this way (see synchronicity).

2. in statistics and experimental psychology, a co-occurrence between a response or outcome variable and a variable other than a predictor of interest. —concomitant adj.