Idioms and Phrases with on one's honor
on one's honor
Entrusted to behave honorably and honestly without supervision. For example, The students were on their honor not to consult notes during the exam. Originally alluding to a solemn oath, this idiom dates from the mid-1400s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.