/ Dictionary / Index R registered mail: Meaning and Definition of Find definitions for: reg'istered mail' Pronunciation: [key] prepaid first-class mail that has been recorded at a post office prior to delivery for safeguarding against loss, theft, or damage during transmission. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. registered dietitian registered nurse Related Content Daily Word Quiz: eccentric Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language