I've been thinking about both nemesis and foil, but the problem is that 'nemesis' implies the opponent inevitably wins (or at least that the struggle is endless) and 'foil' (at least in terms of how it's used in philosophical discourse) implies that the opponent is being used to present oneself in a better light. Is there a word for an opponent through whom one defines oneself that doesn't slant one way or the other? "Defining interlocutor" is another suggestion that works well when talking about ideas and identity, but I'd like to find something that would work more broadly, too.
If neither Nemesis nor Foil , yet somewhat identifying role being played, I might suggest
1. a person, group, or force that opposes or attacks; opponent; enemy; foe.
2. a person, group, etc., that is an opponent in a contest; contestant.
It is always hard to paint the connotations beyond the dictionary definitions, however I believe that both Adversary and Rival below say something far more expansive and visceral than opposition alone does.
- consider the feelings from the etymology of it's root advert - Origin and *Etymology of advert Middle English averten, adverten "to notice, think of, consider, be heedful," borrowed from Anglo-French avertir, advertir "to notify, (reflexive) recognize, be mindful of," going back to Vulgar Latin advertīre, alteration (by conjugational shift) of Latin advertere "to turn or direct toward, direct (attention) toward, pay heed (to), attract the attention of," from ad- ad- + vertere "to turn" — more at 1worth from websters
If it were a more friendly competition, where both spur each other forward I would suggest Rival
A person or thing competing with another for the same objective or for superiority in the same field of activity.
‘he has no serious rival for the job’ as modifier ‘gun battles between rival gangs’
1.1with negative A person or thing that equals another in quality.
‘she has no rivals as a female rock singer’
1570s, from Latin rivalis "a rival, adversary in love; neighbor," originally, "of the same brook," from rivus "brook" (see rivulet ). "One who is in pursuit of the same object as another." The sense evolution seems to be based on the competitiveness of neighbors: "one who uses the same stream," or "one on the opposite side of the stream" A secondary sense in Latin and sometimes in English was "associate, companion in duty," from the notion of "one having a common right or privilege with another." As an adjective 1580s from the noun.
The root in rival also captures some of my feeling about the word, that means as much as 'shared consciousness' - occupying the world created by your association as much as the opposition within it.
I think the answer is in the question - opponent.
- A person who attacks, objects to, disagrees with, or resists a policy, institution, doctrine, etc. Frequently with of or to.
In politics, for example, the opposition are there specifically to oppose anything and everything in order to seek out flaws in argument, weaknesses in policy and potential failures in administration.
They sharpen up the ruling party and, if the job is done properly, they will have had a part in the development of that ruling party. They have helped to define that ruling party by their opposition.
Thus the word 'opponent' carries the very meaning which the question requires.
I think what's been overlooked is my [Arch-]Enemy (rather than simply an enemy), capitalisation not really necessary but useful to emphasize the singular, defining nature.
A more idiomatic (but a biblical reference, if you don't mind that) is thorn in [my] side.
If you're not averse to the cultural reference, @hot-licks' suggestion of Moriarty is a good one. Nay, excellent. If you're not a fan of Conan Doyle / Sherlock Holmes, but appreciate the works of Jay Arthur Artol-Keen, then Sauron might work too ;o)