Middle English probably from Old Norse frāper1 in Indo-European roots
American Heritage Dictionary of the English Language, 5th Edition
Fro Sentence Examples
His whole career was taken up with marchings to and fro within the lands, first of the Eastern, then of the Western empire.
Hundreds of little sail-boats swung to and fro close by, and the sea was calm.
I guessed vaguely from my mother's signs and from the hurrying to and fro in the house that something unusual was about to happen, so I went to the door and waited on the steps.
The sound travelled to and fro in the pipes several times before the signals died away, and he found that the velocity decreased with the intensity, tending to a limit for very feeble sounds, the limit being the same whatever the source.