What’s the difference between 字引 and 辞書?
Nothing really, but 字引 is just far less used. From a Stack Exchange post from 2013 I found, someone who had looked this up using the Balanced Corpus of Contemporary Written Japanese got these stats:
辞書 1078件
辞典 919件
字書 65件
字引 37件
字典 26件
total 2125件
They even posted that more than half of the hits for 字引 appeared to be for the word 生き字引 (walking dictionary).
Gotta remember this one!
Yes, then one day you too can be a walking dictionary! 
My nickname at my Japanese school is already C3PO.
Btw, this question is more of a The quick or short Language Questions Thread (not grammar). Did you know about that one?
What is ってきた’s role in 「あ、外雨が降ってきた! れいくんの所も降ってますか?」?I’m pretty sure it’s not the sequential use like “rained and then came” right? And when would we use that instead
降ってます as seen in the second sentence?
It is ! But in a metaphoric way, it “came” toward the speaker in time, from the past to the present, where the speaker currently stand. It’s one of the usage of てくる and it’s used for something that started in the past, gradually continued to the present, and is still going on.
It’s used a lot when someone notice rain, because it fits perfectly, rain started earlier, at first a few droplets, and it became bigger and bigger until the person noticed. Also rain won’t stop suddenly once noticed, it will continue.
降ってます is just 降っています (it’s raining, present progressive) but said in a slightly casual way with the い dropped.
This makes so much sense. Thank you :))
I know that everyone says that 「〜がある〜」 and 「〜のある〜」 mean the same thing but in fact are there any differences in usage and/or nuance?
I can’t think of anything. All I would say is if you have a が inside a relative clause and then you have a が in the main clause as well, it’s going to feel a little less natural if you don’t make that first one a の, since the option is right there for you to do that and it removes the feeling of too many がs… but it’s not required.
見つけられなくてすみませんでした。
I saw this sentence today and the conjugation of it has me somewhat confused. I’ve never run into anything with a negative before て before. Could someone explain this or direct me to something that does please?
なくて is the て-form of ない. This is just like any other い-adjective. For example, the て-form of 楽しい is 楽しくて.
It’s the connective te form in the negative.
I couldn’t find it, and I’m sorry. => I’m sorry I couldn’t find it.
You might have heard it in phrases like 〜なくてもいい and 〜なくてはいけない
There is also 〜ないで, which you use in different contexts. like 〜ないでください (please don’t X), or an example: テレビを消さないで出かけた。(I left without turning off the tv).
And the て form of 楽しくない is 楽しくなくて
Yeah. I think the most important thing to note is that the ない conjugation of verbs (as well as たい) is just an い-adjective and can be treated that way for all subsequent conjugations.
Except you can’t add another negative on there 
I’m pretty sure you can grammatically, regardless of what people actually do.