The term Shiva means ‘Auspicious.
Shiva does not seem to be mentioned in the Vedas.
However Shiva’s Name appears in the Sri Rudra,
‘Namasivaaya Cha. Sivadharaaya cha’
The difficulty arises when tries to identify Shiva with Iswara is the fact that Iswara means Personal God.
Among the six systems of Hindu philosophy, early Samkhya and Mimamsa do not consider the concept of Ishvara, i.e., a supreme being, while later Samkhya, Yoga, Vaisheshika,Vedanta and Nyaya believe in the existence of an Ishvara..
It is in origin, The term ‘Shiva’ a nominalized adjective meaning “capable, able, being in control”, like īśa “owning, possessing” derived from a root īś- “to own, possess; rule over”, ultimately cognate with English own (Germanic *aigana-, PIE *aik-). The theological meaning “the Supreme Being” first arises in the Manu Smriti, while īśa is used as a name of Rudra somewhat earlier, in the Shvetashvatara Upanishad(c. 300 BCE), considered the first evidence of the development of that deity, the later Shiva, into a supreme, cosmological god.
In Saivite traditions of Hinduism, the term is used as part of the compound “Maheshvara” (“great lord”) as a name for Shiva. In Mahayana Buddhism it is used as part of the compound “Avalokiteśvara” (“lord who hears the cries of the world”), the name of a bodhisattva revered for her compassion. When referring to divine as female, particularly in Shaktism, the feminine Īśvarī is sometimes used.
According to Purans Shiva is different from Rudra, Rudra being an Amsa, Manifestation of a part of Shiva.
Shiva has been given the following Prime Attributes in terms of functionality,
- (Thrikaakgni) Kaala,
- (Kallakgni) Rudra,
Rudra is one among and Chief of 11 Rudras, Ekadasa Rudras,
The Vamana Purana describes the Rudras as the sons of Kashyapa and Aditi.
Here they are named Nirriti, Shambhu, Aparajita Mrigavyadha, Kapardi, Dahana, Khara, Ahirabradhya, Kapali, Pingala and Senani – the foremost. The Harivamsa, an appendix of the Mahabharata, makes Kashyapa and Surabhi – here, portrayed as his wife – the parents of the Rudras. In another instance in the Mahabharata, it is Dharma (possibly identified with Yama) who is the father of the Rudras and the Maruts.
The furious Rudra was in Ardhanari form, half his body was male and other half female. He divided himself into two: the male and female. The male form then split itself into eleven, forming the eleven Rudras. Some of them were white and gentle; while others were dark and fierce.
They are called Manyu, Manu, Mahmasa, Mahan, Siva, Rtudhvaja, Ugraretas, Bhava, Kama, Vamadeva and Dhrtavrata.
From the woman were born the eleven Rudranis who became wives of the Rudras. They are Dhi, Vrtti, Usana, Urna, Niyuta, Sarpis, Ila, Ambika, Iravatl, Sudha and Diksa. Brahma allotted to the Rudras the eleven positions of the heart and the five sensory organs, the five organs of action and the mind.Other Puranas call them Aja, Ekapada (Ekapat), Ahirbudhnya, Tvasta, Rudra, Hara, Sambhu, Tryambaka, Aparajita, Isana and Tribhuvana.
While Kapalin is described the foremost of Rudras here, in theBhagavad Gita – a discourse by the god Krishna in the epic – it is Sankara who is considered the greatest of the Rudras. Both Kapalin and Sankara are epithets of Shiva
.In another instance, they are described as sons of Tvastr and named: Vishvarupa, Ajaikapad, Ahi Budhnya, Virupaksa, Raivata, Hara, Bahurupa, Tryambaka, Savitra, Jayanta and Pinakin.
While usually the Rudras are described to eleven, in one instance in the Mahabharata; they are said to be eleven thousand and surrounding Shiva.
The eleven groups of hundred are named: Ajaikapad, Ahi Budhnya, Pinakin, Rta, Pitrrupa, Tryamabaka, Maheshvara, Vrsakapi, Sambhu, Havana and Ishvara..
It seems to me that though Shiva is not mentioned in the Vedas directly,considering the meanings of the Attributes to the Nirguna Brahman,
The Reality, it would seem that the term Shiva is an indicator of the Nirguna Brahman in its entirety without Name and Form but called as Shiva to
enable us to understand the Concept of Nirguna Brahman as Auspicious.