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[Linus]

From this site: http://cydathria.com/ms_donna/tg_def.html

Cisgender

The term Cisgender was coined in 1995 by Carl Buijs, a female-to-male transsexual from the Netherlands.

• Main Entry:cis- Function:prefix Etymology:Latin, from cis Meaning: 1: on this side <cislunar> 2:usually ital : cis <cis-dichloroethylene> -- compare TRANS- 2b

As we are not talking about chemistry, it is definition 1 that we want.
As we defined gender above to mean "the behavioral, cultural, or psychological traits typically associated with one sex", Cisgendered literally means: on this side of the behavioral, cultural, or psychological traits typically associated with one sex.
Stated simply, it means that one's identity and presentation matches their physical morphology.