"Non-significant" or "not significant" variable?
@PeterShor's comment is also correct from a statistical point of view. Generally, though, we refer to the significance of a test statistic not a variable since there is no way to test whether a variable is significant, only a relationship, comparison, difference, etc. So, for example, in a regression model of y on x, the coefficient on x is non-significant | not significant. The x variable cannot be significant on its own.