Nwir, n. sky, the area containing the clouds and celestial objects. The physical sky as opposed to the ground.
Poini, n. heaven, bliss, a feeling of complete satisfaction and well-being. Metaphysical concept of heaven, Elysion, blissfulness.
In this case the differentiation is between two words to refer to "sky, heaven". The first one is more physical than the last one. But the difference doesn't end there. In Tulvan thought they don't think of the sky as a place of rest for the glorious dead or as a reward. They believe in states of mind, so the "heaven" is a state of mind, which can be said of a number of situations. To have a good idea can be refered as having a "heaven-like moment", or even that kind of warm feeling of happiness can be rendered as poini. The idea of heaven being the upper skies would be puzzling to all Tulvans.
It has been noted the similarity between this word, poini, and other words, such as poilu, approximately meaning our "logic". To Tulvans having high reason and logic is the closest they can think of being in heaven or bliss. Wether this words were related in long lost past or if it's a coincidence is now a lost knowledge. Needless to say many speakers of this language would like to think so nonetheless.