Sepoy
A sepoy () was originally the designation given to an Indian infantryman armed with a musket in the armies of the Mughal empire.

In the 18th century the French East India Company and its other European counterparts employed locally recruited soldiers within India, mainly consisting of infantry designated as "sepoys". The largest of these Indian forces, trained along European lines, was that belonging to the British East India Company.
  
The term "sepoy" is still used in the modern Nepalese Army, Indian Army and Pakistan Army, where it is used for the rank of private soldier.

Etymology
The term sepoy is derived from the Persian word  () meaning the traditional "infantry soldier" in the Mughal Empire, these infantrymen were armed with a Rifle and a Talwar they wore the colors of the "Great Moghul" and relied upon War elephant for transport and carriage and even operated artillery pieces and even Rocket. 

In the Ottoman Empire the term  was used to refer to horse Cavalry Corp.

The French East India Company was the first to employ local sepoy to fight for foreign interests within Indian soil during the Carnatic Wars. Soon other European powers did the same, to protect their interests.

In its most common application, sepoy was the term used in the British Indian Army, and earlier in that of the British East India Company, for an infantry private (a cavalry trooper was a ).

Historical usage
The term sepoy came into use in the forces of the British East India Company in the eighteenth century, where it was one of many, such as peons, gentoos, mestees and topasses used for various categories of native soldier. Initially it referred to Hindu or Muslim soldiers without regular uniform or discipline. It later generically referred to all native soldiers in the service of the European powers in India. Close to ninety-six percent of the British East India Company's army of 300,000 men were native to India and these sepoys played a crucial role in securing the subcontinent for the company.

Equipment
The earliest Sepoy used Matchlock rifle and operated bulky and inefficient cannon. During the time of Babur when archery was more common. Much had not changed by the time of Akbar when chivalry became the norm.

By the time of Aurangzeb the Mughal Empire had advanced significantly and utilized all assets to annex lands.

During the Carnatic Wars the Mughal Empire saw much more advanced types of Musket. By the Anglo-Mysore Wars, Blunderbuss were deployed along with Rocket.

History

Mughal Empire 16th-18th centuries

A Sipahi or a sepoy was an infantryman armed with a musket in the army of the Mughal Empire. 

The earliest sepoys were armed with daggers, talwars and matchlocks. By the mid to late 17th century they began to utilize more upgraded forms of muskets and even rockets. These sepoys also operated artillery and used war elephants for transport, hauling artillery and in combat.

Under Babur, Humayun, Akbar, and Aurangzib sepoys were known as tabinan (cavalry trooper), and dakihili (infantrymen). Sepoys became even more visible when they gained European arms and fought for various fragmented polities of the Mughal Empire during the Carnatic Wars. By the 18th century nawabs had their own sepoy units and so did the European merchant companies in India.

Sepoys in British service

The East India Company initially recruited sepoys from the local communities in the Madras and Bombay Presidencies. The emphasis here favored tall and soldierly recruits, broadly defined as being "of a proper caste and of sufficient size". In the Bengal Army however, recruitment was only amongst high caste Brahmin and Rajput communities, mainly from the present day  Uttar Pradesh and Bihar regions. Recruitment was undertaken locally by battalions or regiments often from the same community, village and even family. The commanding officer of a battalion became a form of substitute for the village chief or gaon bura. He was the mai-baap or the "father and mother" of the sepoys making up the paltan (from "platoon"). There were many family and community ties amongst the troops and numerous instances where family members enlisted in the same battalion or regiment. The izzat ("honour") of the unit  was represented by the regimental colours; the new sepoy having to swear an oath in front of them on enlistment. These colours were stored in honour in the quarter guard and frequently paraded before the men. They formed a rallying point in battle. The oath of fealty by the sepoy was given to the East India Company and included a pledge of faithfulness to the salt that one has eaten.

The salary of the sepoys employed by the East India Company, while not substantially greater than that paid by the rulers of Indian states, was usually paid regularly. Advances could be given and family allotments from pay due were permitted when the troops served abroad. There was a commisariat and regular rations were provided. Weapons, clothing and ammunition were provided centrally, in contrast to the soldiers of local kings whose pay was often in arrears. In addition local rulers usually expected their sepoys to arm themselves and to sustain themselves through plunder.

This combination of factors led to the development of a sense of shared honour and ethos amongst the well drilled and disciplined Indian soldiery who formed the key to the success of European feats of arms in India and abroad.

Following the Indian Rebellion of 1857 the surviving East India Company regiments were merged into a new Indian Army under the direct control of the British Crown. The designation of "sepoy" was retained for Indian soldiers below the rank of lance naik, except in cavalry where the equivalent ranks were sowar or "trooper".

Sepoys in French service
Following the formation of the French East India Company () in 1719, companies of Indian sepoys () were raised to augment the French regulars and Swiss mercenary troops available. By 1720 the sepoys in French service numbered about 10,000. Although much reduced in numbers after their decisive defeat in India at the Battle of Wandewash in 1760, France continued to maintain a Military Corps of Indian Sepoys () in Pondicherry until it was disbanded and replaced by a locally recruited gendarmerie in 1898.
The 19th century diplomat Sir Justin Sheil commented about the British East India Company copying the French Indian army in raising an army of Indians:

Sepoys in Portuguese service
Sepoys were also recruited in Portuguese India.  The term  (sepoy) was also applied by the Portuguese to African soldiers in Angola, Mozambique and Portuguese Guinea, plus African rural police officers.  from Angola provided part of the garrison of Goa during the final years of Portuguese rule of that Indian territory.

Other usages
The same Persian word reached English via another route in the forms of  and .  , the Basque version of the word, is used by leftist Basque nationalists as an insult for members of the Basque Police, implying that they are not a national police of the Basque region due to their connection with the Spanish government.

In Hispanic American countries, especially in Argentina, the word  has historically been used as a pejorative colloquial expression referring to individuals considered as serving foreign interests, as opposed to serving their own country.