- isotropicHaving properties that are identical in all directions; exhibiting isotropy
- isothermA line on a graph or chart, such as a weather map, along which all the points have the same temperature.
- isochronousHappening at regular intervals; isochronal.
- isobarA line drawn on a map or chart connecting places of equal or constant pressure.
- iso-Same, identical.
- isochronalHaving the same duration.
- isochronyThe state of being isochronous.
- isoglossA line on a map indicating the geographical boundaries of a linguistic feature.