Merriam-Webster's Collegiate® Dictionary, 11th Edition
EARNEST
I. noun
Etymology: Middle English ernest, from Old English eornost; akin to Old High German ernust earnest Date: before 12th century a serious and intent mental state , a considerable or impressive degree or amount ,
II. adjective Date: before 12th century characterized by or proceeding from an intense and serious state of mind, grave , important , see: serious earnestly adverb earnestness noun
III. noun
Etymology: Middle English ernes, ernest, from Anglo-French arres, erres, plural of erre earnest, from Latin arra, short for arrabo, from Greek arrhabōn, of Semitic origin; akin to Hebrew ‘ērābhōn pledge
Date: 13th century
something of value given by a buyer to a seller to bind a bargain, a token of what is to come ; pledge