happenstance (n.)

mid-15c., "chance, luck," verbal noun from happen (v.); meaning "an occurrence" is 1550s. Sense of "spontaneous event or display" is from 1959 in the argot of artists. Happenings "events" was noted by Fowler as a vogue word from c. 1905.

c. 1200, "a fact related to another fact and modifying it without affecting its essential nature" (originally in reference to sins), from Old French circonstance "circumstance, situation," also literally, "outskirts" (13c., Modern French circonstance), from Latin circumstantia "surrounding condition," neuter plural of circumstans (genitive circumstantis), present participle of circumstare "stand around, surround, encompass, occupy, take possession of" from circum "around" (see circum-) + stare "to stand," from PIE root *sta- "to stand, make or be firm." The Latin word is a loan-translation of Greek peristasis.

Meaning "a person's surroundings, environment" is from mid-14c. Meaning "a particular detail, matter of small consequence" is from c. 1300; sense of "that which is non-essential" is from 1590s. Obsolete sense of "formality about an important event, ceremonious accompaniment" (late 14c.) lingers in Shakespeare's phrase pomp and circumstance ("Othello" III, iii), taken by Edward Elgar as the title of his military march (1901), which is a staple of U.S. graduations.