Idioms and Phrases with of old
Formerly, long since, at an earlier time, as in In days of old the whole town turned out to watch the parade. This somewhat archaic idiom dates from about 1400.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.