If you mention something in passing, you mention it briefly while you are talking or writing about something else.

What does it mean to mention in passing?

Definition of mention only in passing

: to refer to only briefly Her contributions were mentioned only in passing.

What does it mean if someone is passing?

You can refer to someone's death as their passing, if you want to avoid using the word 'death' because you think it might upset or offend people. His passing will be mourned by many people. Synonyms: death, demise [euphemistic], decease [formal], passing on or away More Synonyms of passing.