What does Shiva mean?
This is a tricky question and there are numerous definitions but nothing concrete. Lately, I found a good explanation in a book.
“On the authority of Siddhanta Kaumudi and Shabda, Kalpa Dharma, Shiva means, one who makes thin or attenuates sin (asubha-inauspicious).1
An important aspect of Shiva is that he is more human. He has all the qualities and weakness of a human being like compassion, anger, lust etc. In fact, Lord Shiva is a perfect amalgamation of human and supernatural characteristics. In human qualities, he is lover, dancer, fighter and hunter. And in supernatural form, he is the creator and destroyer and man and woman in one – ardhanarishwara. And this is the greatest significance of Lord Shiva.
The worship of Lord Shiva has undergone significant changes. In the Vedic age, Lord Shiva was known as Rudra and occupied important position. But later Brahmanism undermined the importance of Lord Shiva. The reason is obvious the appearance of Lord Shiva with matted locks and ash smeared body which is not in collusion with other beautiful gods. So they did try to beautify Lord Shiva.
But the true nature of Lord Shiva found more prominence as time went by as he is more in contact with nature than any other god. And there is no existence outside nature.
1) Siva The Greatest God, Chitralekha Singh, Prem Nath, Lipika Singh, Publishers Indiana Books, New Delhi