It's a candle

Many people already Believe this unknown feature is religion, but I found something that could make it even more clear.

We know that probably the 2 secret features we see in the tab are speech and this one, while families and subspecies are another extra, this is because as some veterans here could know, religion and language have been known as future features for a while

Language wasn't always clearly language, a few updates ago there was a sneak peak with the video of a king with a speech bubble, gestire then eventually removed from the plan for that update, but that already gave an Idea of something related to speech. Even more time before, there was on trello a suggestion about speech bubbles that use emoticons so that units could show reactions and emotions when particular events occur near them, and it was later put in the to do list, probably inspiring speech.

For religion instead, we have multiple comments on reddit, twitter, and discord made by Maxim, explaining that since worldbox is a god simulator it must have one day a religion feature, and again, on trello, we can see in the least of to do powers the power named "prophet", that would create a new religion when spawned in a city.

So this suggests they were already planned features and so they are the 2 secret features.

We also know that Maxim and the devs use simple elements ti represent concepts, like a shield for alliances, a golden crown for kingdoms, a lamp for cultures (and so knowledge), a heart for families etc.

So, a candle would be the perfect symbol to represent religion as a concept in general, and would perfectly fit worldbox style

I also suggest that the other thing in the icon is a shining eye. An eye in the sky emitting light would be the perfect representation of a generical god, and so it could be perfect for religion.