[too-uh
n-froh] 
adjective, noun, plural -fros.| 1. | back-and-forth: to-and-fro motion. |
| 2. | a continuous or regular movement backward and forward; an alternating movement, flux, flow, etc.: the to-and-fro of the surf. |
[froh] | 1. | Obsolete. from; back. |
| 2. | to and fro, alternating from one place to another; back and forth: The trees were swaying to and fro in the wind. |
| to and fro adv. Back and forth. |
to and fro
Back and forth, as in He was like a caged animal, pacing to and fro. Strictly speaking, to means "toward" and fro "away from," but this idiom is used more vaguely in the sense of "moving alternately in different directions." [First half of 1300s]