/ Dictionary / Index F fathomless: Meaning and Definition of Find definitions for: fath•om•less Pronunciation: (fa'um-lis), [key] — adj. impossible to measure the depth of; bottomless. impossible to understand; incomprehensible: fathomless motives. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Fathometer fatidic Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language