“Cisgendered” quite simply means “not transgendered”. I believe the term is borrowed from organic chemistry.
Isn’t “cis” a Latin root that means “on this side of”?
As in the Roman province of Gallia Cisalpina, “the part of Gaul that’s on this side of the Alps”?
Indeed so - to distinguish between molecules that have the same atomic formula, but the different arrangement of the atoms gives them different chemical properties. “Trans” molecules have the active atoms on opposite sides of the bond, while “cis” molecules have them on the same side:
Cl H
\ /
C=C
/ \
H Cl trans-dichloroethene
Cl H
\ /
C=C
/ \
Cl H cis-dichloroethene
Grim
Which is (I guess) where the chemists got it from…
Grim