The verb capsize means to upset, to overturn.
The earliest occurrences of the verb capsize that I have found are as follows, in chronological order:
1-: From Vocabulaire des Termes de Marine Anglois et François (Paris: L’Imprimerie Royale, 1777), by the French naval administrator and colonial governor Daniel Lescallier (1743-1822):
TO CAPACISE. Verb. act. Renverser ou chavirer quelque chose ; c’est une expression vulgaire.
Note: Because the spelling capacise occurs only in this dictionary, I think that this spelling may indicate that Daniel Lescallier transcribed a word that he heard spoken rather than read in a text.
2-: From a letter to the Editor, by a person signing themself ‘Britain’s Bulwark’, dated Monday 17th April 1780, published in The Kentish Gazette (Canterbury, Kent, England) of Wednesday 19th April 1780:
Z—nds! (cried Phutatorius, when he first felt the heat of the chesnut) A. Z. in your last paper, has hove us all aback! his introduction of an ecclesiastical moon has so capsized our nautical moon, that we cannot determine the true time of the tide, which to navigators is of the greatest consequence. To be sure, A. Z. has compromised the matter very well between the astronomical and the ecclesiastical full moon, in order to settle the true day to be observed for Easter, by the church; but by no means to the satisfaction of the fleet. We have one general rule to go by at sea, where we do not consult almanacks to know the moon’s age, and of course the tides.
3-: From The musical tour of Mr. Dibdin; in which—previous to his embarkation for India—he finished his career as a public character (Sheffield: Printed for the Author by J. Gales, 1788), by the British actor, composer and author Charles Dibdin (bap. 1745-d. 1814):
The first thing that struck my attention was a dispute between the sailors, whether they should take in two or three reefs in the mainsail and foresail, the majority however—being two to one, for our ship’s company consisted of no more than three—was in favour of the two reefs, and presently we were a mile from land. It now blew and rained very hard, and three sailors, who happened to be passengers, came down into the cabin. They were asked by the rest many questions—for an universal terror had began to prevail—and they all agreed that we carried too much sail, but refused to interfere—for they were “not afraid of weather—beside, it was no concern of theirs.” The dissentient voice upon deck was continually heard to exclaim, “don’t you see what short seas she ships. Damme, my lads, but you’ll repent not taking in another reef.” The other two swore she could carry every thing that was set, and declared there was not a cap full of wind, while the first as confidently affirmed ‘it blew like the devil.’ For my part, I always think that if those who manage the ship do not feel themselves in danger, I have no right to fancy I am; but here being evidently a difference of opinion, and the squalls so frequent, strong, and sudden, I own I began to think, with the sailors below, that there was certainly a chance of “our being capsized.”
4-: From The Caledonian Mercury (Edinburgh, Midlothian, Scotland) of Monday 12th December 1791:
DONAGHADEE, NOV. 20.
A brig, apparently a stranger, was directing her course in here to avoid the danger of the tempest, and from the course she steered, must have come into foul ground, and inevitably been lost. Four of our inhabitants, ever ready to assist strangers, William Hill, Oliver M‘Fadin, Thomas Lindsay, and William Smith, humanely took a yawl and rowed round the pier head to bring the brig safe in, when one of the tremendous seas broke upon and capsized her.
5-: From The Federal Gazette and Philadelphia Advertiser (Philadelphia, Pennsylvania) of Saturday 8th December 1792:
Spoken by Mr. DUBERVAL, in the Character of a SAILOR,
At the New Theatre in Lymington, after the Representation of the Dramatist, performed at the Request of a Gentleman of the Navy.
Said to be written by the Rev. Mr. D—S.
True to his Sovereign, Jack will never flinch,
A British Seaman’s loyal ev’ry inch;
To capsize Kings, † he thinks is not so civil,
And hates your politicians like the Devil.
† Alluding to the dethronement of the French King.
6-: From a letter by a person signing themself ‘Ironicus’, published in the Gazette of the United States and Evening Advertiser (Philadelphia, Pennsylvania) of Thursday 30th January 1794:
Be it known, that one general and universal change ought to take place—revolution is the word—Revolve, revolve and revolve, till all the pleasing, comforting, heart-consoling and exhilerating [sic] delights of capsizing, topsy-turvying, undermining, disjointing and overthrowing all the systems, principles, and practices of this wretched country, are fully realized and enjoyed.
7-: From the American Apollo (Boston, Massachusetts) of Thursday 18th September 1794:
HUDSON, Sept. 4.
Extract of a letter from a person belonging to this city, dated Brest 29th June, 1794, to his friend here.
“I wrote you from St. Maloes, but am fearful my letter did not come to hand, I arrived at this port 10 days ago, in the frigate Le Resolu, of 36 guns, who captured the vessel I belonged to in the channel on 15th ult and sent her into this port, but detained me on board the frigate. The captain offered me the command of a gun, and having presented me with a suit of naval regimentals, a pair of pistols, a sword, and a liberty cap, I consented to take charge of it, we were then standing for an English frigate—at half past four the engagement commenced the first broadside we received killed 23 of our men every man was killed at my gun except myself.
We then wore short round and hauled our wind, and got his three masts in one, hove our main and mizen topsails to the mast, and poured in our whole broadside, which killed upwards of 50 men, and cut away his mizzen and maintop mast, he then hauled down his colours, and in 5 minutes set them again, and kept them set until he shot away our foretop mast, and killed 6 men on our forecastle, we gave another broadside and grappled him; he immediately struck his colours, we then took possession of his ship, capsized his colours and sent him to Brest.
The verb capsize is of unknown origin.
In An Etymological Dictionary of the English Language (Oxford: The Clarendon Press, 1910), the British philologist Walter William Skeat (1835-1912) wrote that capsize may be an alteration of Spanish capuzar or of Provençal cabussado, both apparently derived from Latin caput, denoting the head:
CAPSIZE, to upset, overturn. (Span.?–L.) First in Dibdin (1788). Perhaps a nautical corruption of Span. capuzar, to sink; as in capuzar un bajel, to sink a ship by the head; or of mod. Prov. cabussado, the act of diving, an upset (Mistral 1); apparently derivatives of L. caput, the head. (A guess.)
1 This refers to Dictionnaire Provençal-Français, by the French lexicographer Frédéric Mistral (1830-1914).
The British philologist Ernest Weekley (1865-1954) elaborated on Skeat’s hypothesis in Etymologies, chiefly Anglo-French. Read at the Meeting of the Philological Society on February 4, 1910, published in Transactions of the Philological Society (London: Published for the Society by Kegan Paul, Trench, Trübner & Co., Ltd., 1910):
Capsize.—Earliest record in N.E.D. is 1788. I cannot throw much light on this mysterious word, but I can give a slightly earlier occurrence and an unrecorded form. Lescallier (1777) has ‘to capacise, verb act. Renverser ou chavirer quelque chose ; c’est une expression vulgaire.’ The regular nautical word up to the nineteenth century seems to have been ‘overset,’ and capsize is not even in Jal. The analogy of F. chavirer, faire capot, Sp. capuzar, It. capo volgere suggests that the first element means ‘head’; and this is confirmed by L.G. koppseisen, which Professor Kluge tells me does not occur before about 1850. Here, consciously or not, the L.G. ‘kopp, head,’ has been substituted for cap in the English word. I should guess that the word will be found to belong to the south coast of France. Provençal is particularly rich in compounds of cap, with an adj. or past participle, e.g. capcaudat, capclin, capcorp, capcubert, capdescubert, capdreit, capenclin, capfinit, capras, captondut, captrencat, but these are all metrical terms (“Leys d’amors”). Is there a Provençal phrase cap-assis, ‘topsy-turvy’? Neither Raynouard, Levy, nor Mistral give anything of the kind. As the first part of this ‘low word’ means head, I am inclined to guess that the second part has some connexion with the head’s antipodes, and that the word is a vulgarism of the same type as Du. ‘bolærsen, in caput devolvi, clunibus in altum sublatis’ (Kilian 2).
2 This refers to Etymologicum Teutonicæ linguæ: sive Dictionarium Teutonico-Latinum, a Dutch-Latin dictionary by the Dutch lexicographer Cornelis Kiliaan (1528-1607). The Dutch verb bolaersen means to turn topsy-turvy. In the Latin phrase, the image is: to turn arse over head.