Earnest
Old English eornoste (adjective), eornost (noun), of Germanic origin; related to German Ernst (noun).
wiktionary
From Middle English ernest, eornest, from Old English eornest, eornost, eornust(“earnestness, zeal, seriousness, battle”), from Proto-Germanic *ernustuz(“earnest, strength, solidity, struggle, fight”), a derivative of Proto-Germanic *arniz(“efficient, capable, diligent, sure”), from Proto-Indo-European *er-(“to cause to move, arouse, increase”). Cognate with West Frisian earnst(“earnest, seriousness”), Dutch ernst(“seriousness, gravity, earnest”), German Ernst(“seriousness, earnestness, zeal, vigour”), Icelandic ern(“brisk, vigorous”), Gothic 𐌰𐍂𐌽𐌹𐌱𐌰( arniba, “secure, certain, sure”).
The adjective is from Middle English eornest, from Old English eornoste(“earnest, zealous, serious”), from the noun. Cognate with North Frisian ernste(“earnest”), Middle Low German ernest, ernst(“serious, earnest”), German ernst(“serious, earnest”).
Of uncertain origin; apparently related to erres. Compare also arles.
earn + -est
etymonline
earnest (adj.)
"serious or grave in speech or action," early 14c., ernest, from Old English eornoste (adj.) "zealous, serious," or from Old English noun eornost "seriousness, serious intent" (surviving only in the phrase in earnest), from Proto-Germanic *er-n-os-ti- (source also of Old Saxon ernust, Old Frisian ernst, Old High German arnust "seriousness, firmness, struggle," German Ernst "seriousness;" Gothic arniba "safely, securely;" Old Norse ern "able, vigorous," jarna "fight, combat"), perhaps from PIE root *er- (1) "to move, set in motion." The proper name Ernest (literally "resolute") is from the same root. Related: Earnestness.
earnest (n.)
"portion of something given or done in advance as a pledge," early 15c., with unetymological -t- (perhaps from influence of the other earnest), from Middle English ernes (c. 1200), "a pledge or promise;" often "a foretaste of what is to follow;" also (early 13c.) "sum of money as a pledge to secure a purchase or bind a bargain (earnest-money); from Old French erres and directly from Latin arra, probably from Phoenician or another Semitic language (compare Hebrew 'eravon "a pledge"). Sometimes in Middle English as erness, suggesting it was perceived as er "early" + -ness.
