hapchance
Chance, luck, fortune; the random or unplanned quality of an event. (frequently in by hapchance)
literary, rare, uncountable
For the next few minutes he rather neglected the game, the countess absorbing his entire regard. For, by hapchance, the 25 won for her; and, as she took the thirty-five sovereigns, the woman's color deepened, her lips parted, her eyes glowed, and for the moment she looked radiantly happy.
A chance occurrence; an accident, a coincidence.
countable, literary, rare
[…]and yet content to dote upon a line, or the hapchance of a sounding word.
Where it comes from
hap (“luck, fortune, chance”) + chance (“chance, fortune”): a tautological compound, in which both elements independently mean “chance”. Compare the similarly redundant haphazard (hap + hazard), and the synonymous happenchance and happenstance. Recorded from 1866, but attested chiefly in literary prose of the 20th century.
Adapted from the Wiktionary entry hapchance (CC BY-SA 4.0).