"Earnest" is a word in LAW AND LEGAL, ENGLISH

The payment of a part of the price of goods sold, or the delivery of part of such goods, for the purpose of binding the contract Howe v. Hayward, 108 Mass. 54, 11 Am. Rep. 306

To use in earnest.

Something given, or a part paid beforehand, as a pledge;
pledge; handsel; a token of what is to come.

Something of value given by the buyer to the seller, by
way of token or pledge, to bind the bargain and prove the sale.

Intent; fixed closely; as, earnest attention.

Ardent in the pursuit of an object; eager to obtain or do;
zealous with sincerity; with hearty endeavor; heartfelt; fervent;
hearty; -- used in a good sense; as, earnest prayers.

Seriousness; reality; fixed determination; eagerness;
intentness.

Serious; important.