passing

passing adjective [ always before noun ] uk/ˈpɑːsɪŋ/ us
lasting only for a short time and not important

проходящий, мимолетный
a passing interest

PASSING noun

uk/ˈpɑːsɪŋ/ us  the passing of time/years
the way that time passes

течение времени
With the passing of time their love had changed. in passing
If you say something in passing , you talk about one thing briefly while talking mainly about something else.

мимоходом, между прочим
She mentioned in passing that she'd seen Stuart.