Eeshwaraa(Ishwara, sarveshvara, shiva, rajeshwar, maheshwar, sambho shankara, Mahadev, hara) refers to the name of one of the trinity in the Hinduism and is considered as the ultimate Lord of destruction of utmost every thing on the earth. Eeshwara is also referred in short as Eesan or Esha(Isha) and is referred more to the symbol of "linga" (Black stone). He is the most highly worshipped diety equaling Lord Vishnu in power, fame and holds more hindu temples than the vaishnavite supremo Mahavishnu in India and around the world.
The term Eeshwaraa is derived from 2 words "Eesh" and "waraa". 'Eesh' refers to the 'ultimate God' and 'waraa' refers to the 'boon'. So Eeshwaraa also means 'as the one born from the boon of the ultimate God of the entire universe.'
The term Eshwara also means "The Lord." All the major Hindu dieties names ending with Esh, Eshwara denotes that they are referred as "The Lord of the things attached to their names." For instance 1) Ganesh refer to the elephant head of Hindu God who is also termed as "the Lord of elephants." 2) Mayureshwar(Muruga) refers to the brother of Lord Ganesh, Son of Lord Shiva and Goddess Shakti who is also referred as the "Lord of peacocks." 3) Rajeshwar refers to another name of Lord Shiva, which means "Lord of the all the Kings on the earth and the entire universe." 4) Parvateshwar refers to another name of Lord Shiva, which means "Lord of the all the mountains on the earth and on other planets of the universe." 5) Muneshwar (Yogeshwar), another name of Lord Shiva, which means "Lord of the entire saints, holymans, prophets on the earth or any other planet of the universe. 6) Sarveshwar is another name of Lord Shiva meaning "The Lord of the entire Lords of anything and everything on the earth as well as other planets of the universe." 7) Sataneshwar, kapali, bhootnath, Bhairava, Rudra, Mahadev, Maha agori(Agoreshwar) is another popular name of Lord Shiva which means "The master (Lord) of all the bhoots (Ghosts), Satas (Satan), Shudra shakthi (evil powers), Dev, Gandarva, Kinnar(Centuar) Yaksh." So this are the very few popular names of Hindu deities that end with the term Eshwar,indicating that they are the Lords of the respective things or posts associated with their names.
The term Eshwara is a purusha (male) visesha and represents masculinity, It acquires fulfillment and complete empowerment only when it combines with the stree (Female, Feminine) visesha Eshwari (Shakti). Both of them together form the world and run it according to the divine laws of the God. Eshwara, the most fearsome form (Black form) of all the divine entity and the sole entity of destroying things that goes against the nature is always represented by the black stone indicating that "everything is fair in front of justice."