What term describes a long or arduous search for something?

The term that best describes a long or arduous search for something is "quest." This word encompasses the idea of a purposeful and often challenging expedition or journey undertaken in search of a particular goal or object. A quest typically involves significant effort and a sense of aspiration, which aligns well with the notion of it being arduous.

The concept of a quest often carries connotations of adventure and the pursuit of something meaningful, distinguishing it from similar terms. While "journey" may refer to traveling from one place to another, it does not inherently capture the focused and goal-oriented nature of a quest. "Venture" implies taking a chance or undertaking a risky endeavor but does not specifically highlight the element of searching. "Pursuit" can suggest chasing or trying to catch something but may lack the depth of purpose that a quest embodies. Therefore, "quest" is the most appropriate term to describe a long or arduous search for something significant.