to meet by chance, run into

(formal) friend

passing; going by.

time / an event, case, occasion, moment; a specific period in time / a time of something / a season / a tense / (literary) the time during which a narrative takes place

library (building)

contingent, casual, accidental, incidental

by chance, incidentally

chance, contingency

the past / ancient times

(not of a person) old, aged, antiquated