Etymology
c. 1400s, from sound + -ly. Originally meaning "safely", the present sense came in the 16th century.
Adverb
soundly (comparative more soundly, superlative most soundly)
- In a thorough manner; in manner free of defect or deficiency.
He was soundly thrashed by the semi-professional boxer.
1610–1611 (date written), William Shakespeare, “The Tempest”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act IV, scene i], page 16:Pro. Let them be hunted ſoundly : At this houre / Lies at my mercy all mine enemies : […]
1847 October 16, Currer Bell [pseudonym; Charlotte Brontë], chapter IV, in Jane Eyre. An Autobiography. […], volume I, London: Smith, Elder, and Co., […], →OCLC, pages 42–43:Mrs. Reed soon rallied her spirits: she shook me most soundly, she boxed both my ears, and then left me without a word.
1899, William George Aston, A History of Japanese Literature, page 272:The wedding company, fatigued with their enjoyment of the previous night, slept soundly late into the next morning.
1911, L. D. Biagi, The Centaurians, Ch. I:My gold carried little weight with him, he was sincerely fond of me and consequently rated me soundly for all indiscretions, declaring I would regret wasting the best years of my life and deadening my vast talents […]