There is no word of Nakshatra in english and sanskrit word is only used in form of english. since everyday new word is added to english I guess this sanskrit word is also part of now modified english dictionary.
In Sanskrit it is written as नक्षत्र and in english it would be Nakshatra which is a term used for lunar mansion in astrology of Hinduism or in Indian Astronomy. A nakshatra is 27 or 28 equal divisions along the ecliptic.
Nakshatra are the signs or symbols behind each zodiac signs, you can say that there are 2.5 nakshatra behind every zodiac sign, which provides a true image of a someone's personality. you can find 27 nakshatras in the zodiac.