Wiktionary
vb. (context idiomatic English) To avoid confusing or mix up something; to keep something clear or organized.
Usage examples of "keep straight".
Though he had never seen this female alive, and could barely keep straight the number of generations back she had lived, he could imagine her cold gaze being as merciless in life as her shadowed stare was now.
I felt if she would help me to keep straight, that now, with her father and my sister both dead, we might be happy together.
The walkway ended abruptly at the rear wall, as though some fuedal war lord had erected a fortress keep straight across an ancient Roman highway.
As a mark of reference on this line he chose a grotesquely torn spot of the wall since it was almost impossible to keep straight under the conditions of weightlessness without such a fixed point.
The important thing, the only thing you have to get straight and keep straight, is that they have plenty of reasons to kill us.