parlous (adj.)

c. 1300, "full of danger; risky; involving exposure to death, destruction or injury," also "spiritually dangerous," from Old French perillos "perilous, dangerous" (Modern French périlleux), from Latin periculosus "dangerous, hazardous," from periculum "a danger, attempt, risk," with instrumentive suffix -culum and first element from PIE *peri-tlo-, suffixed form of root *per- (3) "to try, risk." In Arthurian romances, the sege perilous (c. 1400) was the seat reserved for the knight who should achieve the quest of the Grail. Related: Perilously; perilousness.

Proto-Indo-European root meaning "to try, risk," an extended sense from root *per- (1) "forward," via the notion of "to lead across, press forward."

It forms all or part of: empiric; empirical; experience; experiment; expert; fear; parlous; peril; perilous; pirate.

It is the hypothetical source of/evidence for its existence is provided by: Latin experiri "to try," periculum "trial, risk, danger;" Greek peira "trial, attempt, experience," empeiros "experienced;" Old Irish aire "vigilance;" Old English fær "calamity, sudden danger, peril, sudden attack," German Gefahr "danger," Gothic ferja "watcher.