What is the meaning of "及"

Hello.
I have been reading a lot about the Meiji constitution in the last few days.
What I noticed is, that they replaced every hiragana with katakana, the usage of 之 and 其れ
as their kanji variant, not hard to grasp. But the usage of 及 confused me, stretch doesn’t make sense in this
context.

Maybe some kind of officious “and”, like here: グレートブリテン及び北アイルランド連合王国, for example?

Yep, kanji dictionary says “and, as well as”. Reading is およ(び).

Oh, I didn’t know, that 及 alone also means “and, as well as”
I was only aware of 及ビ.
Thanks for helping!

It’s not precisely correct to straight out say 及=and, but in formal writing you can sometimes omit okurigana.

Also, this was before orthographic reform. That’s obvious from using katakana for okurigana, but there are other things that got reformed as well, such as kanji forms, usage and readings.