/ Dictionary / Index F fth.: Meaning and Definition of Find definitions for: fth. Pronunciation: [key] fathom. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. FTC ft-L Related Content Daily Word Quiz: entomology Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language