“Dive” = “fly into”?

Question

The words 飛ぶ and 跳ぶ are both read as とぶ, the former meaning "to fly" and the latter meaning "to jump" (generally; don't know if they are interchangeable at all).

The compound-verb suffix 〜込【こ】む means that the action "goes in (to)", "enters", etc.

So the word とびこむ means "to jump/dive into", both literally and figuratively ("jump into (doing) a mountain of homework", "butt in to someone's business", etc.).

However, とびこむ is written with the "to fly" version of the kanji: 飛び込む.

Why is this? When 跳ぶ means jump and 〜込む means "into", why wasn't 跳 chosen for とびこむ? This doesn't make sense to me at all.

Answer 1

飛ぶ is the general term that covers all the uses of homophonous kanjis such as 跳ぶ and 翔ぶ. 跳ぶ is a specific one, entailing some mid-air movement (such as pedaling your legs, etc.). As usual with homophonous kanjis, the specific one can be replaced by the general one, but not the other way around. In the literal sense "to dive in to e.g. a swimming pool", you can use 飛び込む as well as 跳び込む. For the metaphoric sense "jump into homework/business", 跳ぶ is probably too specific because those senses do not accompany movement in the air, and you have to use the general 飛ぶ.