By accident:
— Betrayed by a word haply overheard.

synoniemen: by chance, by luck.

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