By chance:
— We may possibly run into them at the concert.

synoniemen: maybe, mayhap, peradventure, perchance, perhaps.

Roget 470: possibly, by possibility; perhaps, perchance, peradventure; maybe, may be, haply, mayhap.    if possible, wind and weather permitting, God willing, Deo volente [Lat.], D.   V.; as luck may have it.    ... meer laten zien

To a degree possible of achievement or by possible means.