The word 'passion' is one of the most dramatically transformed words in the English language: it began as a word for agony and became a word for desire. It entered English in the twelfth century from Old French 'passion,' from Late Latin 'passiō' (suffering, enduring, submission), from 'passus,' the past participle of 'patī' (to suffer, to endure, to undergo, to allow), from PIE *peh₂- (to hurt, to damage). For its first four centuries in English, 'passion' meant almost exclusively 'the suffering and death of Jesus Christ' — the Passion narrative, Passion plays, Passion music (Bach's 'St. Matthew Passion').
The secular broadening — from 'suffering' to 'any intense emotion' — unfolded gradually during the late medieval and early modern periods. The theological reasoning behind the transfer is revealing: in Scholastic philosophy, 'passiones' (passions) were states in which the soul was acted upon by external or bodily forces, as opposed to 'actiones' (actions), which the soul initiated. A passion was something suffered — something that happened to you, that moved you without your consent. Anger, fear, desire, grief,
The Latin verb 'patī' produced a large English family organized around the concept of undergoing and enduring. 'Passive' (being acted upon, not acting), 'patient' (one who endures — originally 'one who suffers,' then 'one under medical care,' then 'one who waits calmly'), 'patience' (the capacity to endure), 'compassion' (suffering with another, com- + patī), 'impassioned' (filled with passion), 'dispassionate' (without passion, objective), and 'compatible' (capable of suffering together, then 'able to coexist harmoniously'). The medical 'patient' and the emotional 'passion' are the same word: both describe someone who undergoes something.
Greek 'páthos' (πάθος, suffering, feeling, experience) is a cognate from the same PIE root, and it produced its own massive English family: 'pathos' (the quality of evoking pity or sadness), 'pathology' (the study of suffering/disease), 'sympathy' (feeling with, syn- + pathos), 'empathy' (feeling into, en- + pathos), 'apathy' (without feeling, a- + pathos), 'antipathy' (feeling against), 'telepathy' (feeling from afar), and the medical suffix '-pathy' (disease, treatment). The Greek and Latin branches reinforce each other: 'passion' and 'pathos,' 'compassion' and 'sympathy,' 'impassive' and 'apathetic' are near-synonyms from the same PIE root through different channels.
The modern popular sense — 'passion' as intense enthusiasm ('she has a passion for music,' 'follow your passion') — is the furthest point from the original meaning. Where Latin 'patī' meant helpless endurance, modern 'passion' implies active pursuit. Where the Scholastics treated passions as dangers to rational self-governance, motivational culture treats passion as the precondition for a meaningful life. The word has rotated 180 degrees: from something you