/ Dictionary / Index F first law of thermodynamics: Meaning and Definition of Find definitions for: first' law' of thermodynam'ics. Pronunciation: [key] See under(def. 1). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. first law of motion first lien Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language