Spirit is the recognition that consciousness is ultimately non-individual, our understandings are not localized but rather occurs within societies and cultures as their agency.

My best synonym for spirit and spiritualism would be "unexplained" .

I think it is very difficult to follow the development of the meaning of spirit. It started off in the Bible as 'ruach' - wind, breath. It seems to be understood more as the power inherent in the wind or breath. My understanding of the human body according to the ancient Hebrews is that it has two sources of life - breath and blood. If either is removed, the result is death of the 'nephesh' - the soul in the Old English sense of the word, such as 'all 200 souls on board were lost'.

Here's a curious description of death, detailing the breakdown of the body and the resulting expiration of the body:

Remember Him before the silver cord is snapped, and the golden bowl is crushed, before the pitcher is shattered at the spring, and the wheel is broken at the well, before the dust returns to the ground from which it came, and the spirit returns to God who gave it - Ecclesiastes 12:6, 7.

Ecclesiastes seems to saying that the spirit, the power inherent in breath, returns to God. While Hebrew 'ruach' became Greek 'pneuma', the traditional understanding of what goes back to God is the psyche. Wiki says the Stoics related pneuma and psyche this way:

In its highest form, pneuma constitutes the human soul (psychê, which is a fragment of the pneuma that is the soul of God (Zeus).

I have no problem with using the word spirit or soul if its not used in a religious context. Humans are capable of having complex emotions, convictions and desires and these words reflect that.

I think we have to go to the root of the word, which is Latin Verb spirare (to breathe) or Noun spiritus( breath). Amongst the synonyms is the word essence, which I think sums up the meaning of spirit best.

Just found this on our sister site
[humanist.com]

which I had not visited before

[amazon.com]