Crewman is a generic term for a crew

Crew

A crew is a body or a class of people who work at a common activity, generally in a structured or hierarchical organization. A location in which a crew works is called a crewyard or a workyard...

 member of an aircraft, naval vessel, military unit, or team of professionals attempting to accomplish a goal. In some science fiction

Science fiction

Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 (most notably Star Trek

Star Trek

Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry. The core of Star Trek is its six television series: The Original Series, The Animated Series, The Next Generation, Deep Space Nine, Voyager, and Enterprise...

), Crewman is the lowest military rank on board a spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

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The term "Crewman" may also be related in the non-gender specific form as "crewperson" or "crewmember".