From Longman Dictionary of Contemporary Englishwhite something ↔ out phrasal verbto cover something written on paper, especially a mistake, with a special white liquid so that it cannot be seen anymore → white→ See Verb table
Examples from the Corpus
white out• It stopped, and five men in white clothes got out.• Twenty-five per - cent of whites drop out between the third grade and eleventh grade.• Your white boys look out for your white boys.• Most of the white migrants came out of California.• Lots of big white trucks out there.• A pretty girl in a white coat came out to him and he reminded her of his appointment.• Black ice in winter and white - outs, too.• Trouble from racists who objected to a white woman going out with a black man. 