There are many words to describe the differences between two things, each being a little different from others, each being used in certain circumstances.
dichotomy: A division or contrast between two things that are or are represented as being opposed or entirely different. “a rigid dichotomy between science and mysticism”.
discrepancy: a lack of compatibility or similarity between two or more facts.”there’s a discrepancy between your account and his”
incongruity: the state of being incongruous or out of keeping. Incongruous means not in harmony or keeping with the surroundings or other aspects of something.
diverge: (of a road, route, or line) separate from another route, especially a main one, and go in a different direction.”the flight path diverged from the original flight plan”
contingency: a future event or circumstance which is possible but cannot be predicted with certainty. This word is often used in “contingency plan” to indicate a plan devised for an outcome other than in the usual plan.
collateral: something pledged as security for repayment of a loan, to be forfeited in the event of a default.”she put her house up as collateral for the bank loan”
juxtaposition: the fact of two things being seen or placed close together with contrasting effect. “the juxtaposition of these two images”
proximity: nearness in space, time, or relationship. “do not operate microphones in close proximity to television sets”
substitute: a person or thing acting or serving in place of another. I’ve been puzzled by the word substitution for a long time. It is a common word but it is not commonly used because in a lot of situations, another word is used to replace “substitution”. It is only commonly used in the phrase “substitute teacher”.
understudy: (in the theater) a person who learns another’s role in order to be able to act as a replacement at short notice. In this situation, the substitute person is called understudy.
interim leader: the substitute leader who will serve in the intervening time before a new leader arrives. Sometimes “acting” is used to indicate that the person is acting for the position but not really holding the position.
temp worker: A substitute worker is often called temp to indicate the temporary status. They can also be called strikebreakers during a strike.
duplicate and copy: I’ve never figured out the difference between the two, but it seems that the native speakers always use “duplicate” in certain situations even if “copy” will do.
body double, stunt double: a body double is a person who substitutes in a scene for another actor.
appropriation: 1. the action of taking something for one’s own use, typically without the owner’s permission. 2. the artistic practice or technique of reworking images from well-known paintings, photographs, etc., in one’s own work.
cultural appropriation: the unacknowledged or inappropriate adoption of the customs, practices, ideas, etc. of one people or society by members of another and typically more dominant people or society.
simile and analogy: a figure of speech involving the comparison of one thing with another thing of a different kind, used to make a description more emphatic or vivid (e.g., as brave as a lion, crazy like a fox ). I’ve always thought simile can be used interchangeably with analogy.
reenactment: the acting out of a past event.
imitation and emulation: I’ve always thought that emulation is a form of imitation plus an intention to compete.
replica: an exact copy or model of something, especially one on a smaller scale. “a replica of the Empire State Building”
look-alike: a person or thing that closely resembles another, especially someone who looks very similar to a famous person. “an Elvis Presley look-alike”
verisimilitude: the appearance of being true or real. “the detail gives the novel some verisimilitude”
impersonate: pretend to be (another person) as entertainment or in order to deceive someone.
“it’s a very serious offense to impersonate a police officer”
spitting image: (informal) the exact double of (another person or thing). “she’s the spitting image of her mother”
doppelganger: Someone who looks spookily like you, but isn’t a twin, is a doppelganger. Originally, this was a type of ghost.
rendezvous: a meeting at an agreed time and place, typically between two people. “Edward turned up late for their rendezvous”. This word is often used in the situation that you feel something is so similar to something else that “”it feels like a rendezvous”.
plagiarism: the practice of taking someone else’s work or ideas and passing them off as one’s own.
throwback: a person or thing having the characteristics of a former time. “a lot of his work is a throwback to the fifties”