What is a "fir tree"?

When can I use the word "officially?"

"Officially" means "formally" or "publicly" in most cases. In the informal context, it's used as an emphasis word to mean "for sure," "completely/definitely," or "obviously." Ex: The government officially declared a state of emergency. (formally/publicly) Ex: My boyfriend and I are officially over. (completely/definitely)

What does "unto" mean?

Nice question! 'Unto' just means 'to'. It's an old-fancy way of saying 'to' and is not commonly used anymore.

I don't understand what this line means, what's it?

Astronauts aren't the heroes they're made out to be on Earth. In fact, there's lots of evidence of astronauts succumbing to alcoholism because they couldn't cope with the difference between the public's adoration and their own self-image as ordinary, flawed mortals. It's an excellent metaphor for a rock star like Elton John – the endless flights and touring, the adulation from total strangers. And when he does return home, he puts on a brave face, trying to fall back into old habits, that he clearly has lost. This line could also allude to the idea that the "trip" itself changed him in ways that they don't realize/know.

What does "getting in a fight" mean? Is it different from just saying "fighting"?

"Getting into a fight" and "fighting" have slightly different meanings. "Getting into a fight" refers to entering a fight because a situation is escalating. "Fighting" refers to a current fight happening. Ex: My sister was making me angry, so I left the house to avoid getting into a fight with her. Ex: I'm fighting with my boyfriend right now, so I'm not talking to him.

As a supporter, what's the origin of the term "fan?"

In terms of "fan" meaning "supporter" it supposedly comes from the word "fanatic," which means someone's extreme admiration for something. Although, some people think it comes from the word "fancy" when describing the people who would watch sports as "fancy" in older times. Ex: Baseball is quite popular among fancy young men. => dated use of "fancy." Ex: Shaun's always been a fitness fanatic.