いよいよ

[DarumaBlue]

I'm having a hard time wrapping my head around いよいよ. I'm guessing it's gitaigo, but what does it really mean?

[Harisenbon]

愈々(P); 愈愈; 愈 【いよいよ】 (adv)
(1) (uk) more and more; all the more; increasingly;
(2) at last; finally; beyond doubt;
(3) (at the) last moment; worst possible time; (P)

Examples:
(1) いよいよ薄暮、もうすぐ宵闇。
It's getting more and more shadowy, soon it will be twilight.

(2) いよいよ千載一遇のチャンスがめぐってきた。
At last a chance in a million arrived.

Can you be more specific about what you don't understand about it?

[coco]

I'm having a hard time wrapping my head around いよいよ. I'm guessing it's gitaigo, but what does it really mean?

If you give us an entire sentence, like Harisenbon-san says, you will see what it means.

As for gitaigo(擬態語), let me say my opinion. 　
I don't think いよいよ is 擬態語．

To distinguish between 擬態語 and 一般語 is sometimes hard even for Japanese native speakers. More difficult thing is to explain why they(=Japanese people) can distinguish 擬態語, because they (we) don't need to think about it.

I think the typical definition of 擬態語 is something like this; a word which (sensuously) describe the condition of thing/person with a mimic sound despite being soundless.

擬態語 【ぎたいご】 (n) {ling} mimetic word; word that mimics something that does not make a sound (e.g. the fluttering of a butterfly's wings)

Thus, たびたび( "ABAB" pattern word) isn't 擬態語 even though it looks like 擬態語.

However, the definition above isn't enough explanation about why I don't think いよいよ is 擬態語. The definition of 擬態語 in 広辞苑 is : a word which expresses (sensuous) impression based on the sense of sight or the sense of touch, etc..

Therefore, 擬態語 is rather used for concrete objects, or phenomena that you are now seeing.

For example;
・ 柳の枝がゆらゆらと風にゆれている。　ゆらゆら＝擬態語
・ (掃除をしたら） 床がピカピカになったよ!　ピカピカ＝擬態語

I think 擬態語 is rather used when you describe your instantaneous impression of an object( include person) or phenomena, while ますます and いよいよ( and so on) are rather used for gradual changes of abstract things.

Note: This is only MY thought.　

Hope my poor English makes sense.

[Harisenbon]

Note: This is only MY thought.　

Hope my poor English makes sense.

You made perfect sense, and I fully agree that いよいよ is probably not 擬態語.