I was using "solid" a bit metaphorically, not necessarily meaning materialized into a human body but just to give a sense of the essence of it in a way that would contrast it with Devi, and solid is the first word that came to mind.

I'm far from an expert on this very ancient religion, but the basic idea is that for each Deva such as Shiva, Vishnu, and Brahma, there is an equivalent Devi - Parvati, Lakshmi, and Saraswati. Devi is the feminine form of the word and Deva is the masculine form.

Ardhanarishvara is the union of Shiva and Parvati into one.

There are definitely a lot of stories about incarnations as avatars to interact in a material form, and considering Shiva just might exist outside of time, simultaneously would probably be a good word to describe him.