Definition of "earnest"

He wrote well in a forcible, colloquial style, with the air of being tremendously in earnest, and full of knowledge which overflowed his pages, tricked out with somewhat boisterous illustrations.

1914, February 13, The Times, Obituary: Canon Augustus Jessopp

Take heed that this jest do not one day turn to earnest.

a. 1587, Philippe Sidnei [i.e., Philip Sidney], “(please specify the page number)”, in Fulke Greville, Matthew Gwinne, and John Florio, editors, The Countesse of Pembrokes Arcadia [The New Arcadia], London: […] [John Windet] for William Ponsonbie, published 1590; republished in Albert Feuillerat, editor, The Countesse of Pembrokes Arcadia (Cambridge English Classics: The Complete Works of Sir Philip Sidney; I), Cambridge, Cambridgeshire: University Press, 1912,

That high All-Seer which I dallied withHath turn'd my feigned prayer on my headAnd given in earnest what I begg'd in jest.

c. 1593 (date written), William Shakespeare, “The Tragedy of Richard the Third: […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act V, scene i]

Let's prove among ourselves our armes in jest, That when we come to earnest them with men, We may them better use.

1602, Pastor Fido, (Please provide the book title or journal name)

Now he that hath wrought us for the selfsame thing is God, who also hath given unto us the earnest of the Spirit.

1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], 2 Corinthians 5:5

The vanity is at once encouraged and gratified; while the present small triumph is too readily taken as earnest for a greater one.

1837, L[etitia] E[lizabeth] L[andon], Ethel Churchill: Or, The Two Brides. […], volume II, London: Henry Colburn, […], pages 152–153

But if all this was viewed by Gladstone and the Cabinet as an earnest of St Petersburg's future good intentions in Central Asia, then disillusionment was soon to follow.

1990, Peter Hopkirk, The Great Game, Folio Society, published 2010, page 365