painとpatientに語源的関連はない
late 13c., peine, "the agony suffered by Christ;" c. 1300, "punishment," especially for a crime, "legal punishment of any sort" (including fines and monetary penalties); also "condition one feels when hurt, opposite of pleasure," including mental or emotional suffering, grief, distress; from Old French peine "difficulty, woe, suffering, punishment, Hell's torments" (11c.), from Latin poena "punishment, penalty, retribution, indemnification" (in Late Latin also "torment, hardship, suffering"), from Greek poinē "retribution, penalty, quit-money for spilled blood," from PIE *kwei- "to pay, atone, compensate
ラテン語 "poena"
mid-14c., paciente, "capable of enduring misfortune, suffering, etc., without complaint," from Old French pacient and directly from Latin patientem "bearing, supporting, suffering, enduring, permitting" (see patience). From late 14c. as "slow to anger, self-restrained, having the temper which endures trials and provocations." From late 15c. as "awaiting or expecting an outcome calmly and without discontent." The meaning "pertaining to a medical patient" is late 14c., from the noun. Related: Patiently.
英語語源辞典によればラテン語 "patientem" 、さらに遡って "pati" (to suffer)。IEでは *pē(i)-が語源という説がある。
痛みと忍耐、関連ありそうな見た目をしていながらまったく関係なかった。