Why do some kanji have furigana that are not valid readings?

Question

In my text I read the sentence:

あなたが体験したよりもっと[巨]{おお}きく、もっと深くさせてくれる力があるからだ。

(furigana is from the text)

I understand 大きく, and I understand some words with 巨　like 巨大. However, when I looked up 巨きく　in a dictionary, I was unable to find anything.

Why do these kind of readings exist; however, they are not in a dictionary?

Answer 1

Basic furigana means, for 絶対{ぜったい}, 'zettai' is how you read 絶対...period.

For the non-standard cases, think of it basically the same way, but with a little twist: for 巨{おお}きく, 'oo' is how I want you to read 巨.

As a deeper example...

泥棒{おまえ}は信用{しんよう}出来{でき}ない。

If this is a line of dialogue, the person is saying "I can't trust you", but the implication is that "you" are a thief, and that is why you cannot be trusted.

When the furigana are not standard, in my experience, the furigana is what is said, and the kanji is what is meant. For your example, there's not a lot of difference between 巨 and おお(きい), but it should be basically the same thing: おお is how it's said, but 巨 is the underlying meaning.