in passing

adjective

1. going by or past; elapsing: He was feeling better with each passing day.
2. brief, fleeting, or fortuitous; transitory: to take a passing fancy to something.
3. done, given, etc., in passing; cursory: a passing mention.
4. surpassing, preeminent, or extreme.
5. indicating satisfactory performance in a course, on a paper, in a test, etc.: a passing grade on a test.

adverb

6. surpassingly; exceedingly; very.

noun

7. the act of a person or thing that passes or causes something to pass.
8. a means or place of passage.

Idioms

9. in passing, by the way; incidentally: The speaker mentioned his latest book in passing.

adjective

1. transitory or momentarya passing fancy
2. cursory or casual in action or mannera passing reference

adverb, adjective

3. archaic to an extreme degreethe events were passing strange

noun

4. a place where or means by which one may pass, cross, ford, etc
5. a euphemism for death
6. in passing by the way; incidentallyhe mentioned your visit in passing

adv.

“in a (sur)passing degree, surpassingly,” late 14c., from pass (v.).

n.

“death,” 1869, verbal noun from pass (v.).

Incidentally, by the way, as in “It may be remarked in passing” (Charlotte Brontë, Shirley, 1849). [Mid-1800s]