“both,” “on both sides” — quantitative/directional prefix
The word entered English in the 1500s as ambi- (prefix), borrowed from Latin ambi- — literally “both.” The root ambi (“both”) connects ambi- to the entire dual-directional roots: ambidextrous (ambi- + dexter → skillful with both hands), ambivalent (ambi- + valentia → having both values/conflicting feelings), and ambiguous (ambi- + agere → driven both ways/uncertain). The quantitative prefix ambi- is productive in psychological, anatomical, and general descriptive terminology: e.g., ambilateral, ambisextrous, and ambivert.