In Spanish, from the noun cámara (from Latin camera), meaning a chamber, a room, was derived the collective feminine noun camarada, a military term attested in the mid-16th century in the sense of chambered or cabined (company). (The French feminine noun chambrée, from chambre, room, has the same meaning.) In Spanish, camarada came to be also applied as an individual masculine noun to a soldier who is one’s chamber-fellow (in which sense it was sometimes altered into the masculine form camarado). (Italian adapted the Spanish word in both its meanings and genders as camerata.)
In the second half of the 16th century, the Spanish word was adapted in French as camarade, also camerade, feminine in the collective sense, masculine in the individual one. Randle Cotgrave was only aware of the collective use when he published A Dictionarie of the French and English Tongues in 1611:
Camerade, feminine: A Camerade, or chamberfull; a companie that belongs to, or is euer lodged in, one chamber, tent, or cabin.
In the late 16th and early 17th centuries, English borrowed and adapted the French and Spanish words in their sense of a chamber-fellow, whence English forms such as camerade, camarada, camerado, commorade, comerade and comrade.
The first known use (and definition) of the English word is found in The arte of warre Beeing the onely rare booke of myllitarie profession: drawne out of all our late and forraine seruices, by William Garrard Gentleman, who serued the King of Spayne in his warres fourteene yeeres, and died anno. Domini. 1587, published in 1591:
A Souldier in Campe must make choise of two, or thrée, or more Camerades, such as for experience, fidelity, and conditions, do best agrée with his nature, that be tryed Souldiers and trustie friendes, to the intent that like louing brethren, they may support one another in all aduerse fortune, & supply each others wants. As for example, hauing marched all day, and comming at night to the place where they must encampe, one of them chooseth out the dryest and warmest plot of ground he can get in the quarter, which is appointed to his band for lodging place, doth kéepe all their Clokes, Armes and Baggage, whilest another makes prouision with one of their boyes, in some adioyning Uillage (if time and safety from the Enemie doth permit) for long straw, both to couer their Cabbin, and make their bedd of: during the time that an other with a litle Hatchet, which with a Lether Bottel for drinke, a litle Kettle to séeth meat in, and a bagge of Salt, which are to be borne of the Boyes amongest other Baggage, and are most necessarie things for encamping, doth cut downe forked Bowes and long Poales to frame and reare vp their Cabbin withall, and prouide timber or firewood, if it be in Winter, or when neede requires, whilst an other doth visite Viuandiers and Uictualers (if any follow the Campe) for bread, drinke, and other eates, if otherwise they be not prouided by forrage or Picorée, and makes a hole in the earth, wherein hauing made a fire, stroken two forked stakes at either side, and hanged his Kettle to seath vpon a cudgel of wood vpon the same or that for rost meat he makes a spit, woodden Gawberds, &c. And whilst thus euery one is occupied about their necessarie occasions at one instant, they may in due time make prouision for all their wantes, and by meanes of this league of amitie amongst them, enioy a sufficient time to rest their wearied bodyes, which otherwise would be hard to be done.
One of the early users of comrade as a non-military term was the English buccaneer and explorer William Dampier (1651-1715) in A New Voyage round the World (1699 edition):
There is a kind of begging Custom at Mindanao [in the Philippines], that I have not met elsewhere with in all my Travels ; and which I believe is owing to the little Trade they have ; which is thus : When Strangers arrive here, the Mindanao Men will come aboard, and invite them to their Houses, and inquire who has a Comrade, (which word I believe they have from the Spaniards) or a Pagally, and who has not. A Comrade is a familiar Male-friend ; a Pagally is an innocent Platonick Friend of the other Sex. All Strangers are in a manner oblig’d to accept of this Acquaintance and Familiarity, which must be first purchased with a small Present, and afterwards confirmed with some Gift or other to continue the Acquaintance : and as often as the Stranger goes ashore, he is welcome to his Comrade or Pigally’s House, where he may be entertained for his Money, to eat, drink, or sleep ; and complimented, as often as he comes ashore, with Tobacco and Betel-Nut, which is all the Entertainment he must expect gratis.
In the late 19th century, comrade came to be used by socialists and communists as a prefix to the surname, to avoid such titles as Mr.; hence comrade in the sense of a fellow socialist or communist. For instance, on 12th January 1889, The Comonweal, the official journal of the Socialist League, published a report from Edinburgh containing the following:
At twelve o’clock the new year was inaugurated with resounding cheers for the Social Revolution. A gratifying feature of the evening was the presence of a number of our German comrades, who sang and contributed much to the heartiness of the proceedings. Our comrade Dr. Reddie, Edinburgh, addressed the meeting in English and German. On Sunday last, [...] our usual Sunday evening meeting of members took the form of a tea party. Comrade R. F. Muirhead was in the chair, and the sanctity of the Scottish Sabbath was invaded by songs and recitations, revolutionary and humorous. During the evening, comrade J. Bruce Glasier was presented with a token of the member’s esteem and recognition of his services to the Cause.