So I've been seing this a lot in the sentences I'm doing. You have verbs like:

申し込む
買い込む
閉じ込む

So we're obviously taking the verb stem and adding 込む (to be crowded). What does this suffix actually mean in this context? What does it do to decorate the stem verb?

Insight much appreciated

These might help:
http://www.zanthan.com/japan/nihongo/arc...01910.html
http://www.japanesepod101.com/forum/view...php?t=1345

They sure do - thanks!

There's hundreds of them. After a while you kind of get a sense of what it means but they are they are words in their own right. It pays to look every new one you come across up and treat it as a word (cos it is). It's really just a compound verb. Similar to verb stem + 出す

Sometimes compound verbs of the form verb-stem + verb are a predictable meaning based on the suffix (eg X+はじめる is 'start to X'), but a lot of them aren't, and as mezbup says +込む is in the latter category. So there's no particular fixed relation between the two verbs, and sometimes (as with 落ち込む : to feel sad) you can't predict the meaning at all.

There's a loose analogy with English verb+preposition compounds (eg put up, shut up, wake up...)

Your three examples show this problem mezbup and pm215 are talking about well. here's my "literal" translations:

申し込む - to be called in? to say in? Well, i'd say that 込む has the "into" meaning here, as in the third word, but more abstract.
買い込む - to be engrossed in buying
閉じ込む - to close in (to lock something up)

I think Fishfaces links are bad, because they are trying to give one explanation to the 込む suffix and are failing. It obviously doesn't mean "engrossed in" in 閉じ込む, and it doesn't mean "included" either, so both those links missed that whole meaning which is used in other combinations as well, such as 踏み込む. I didn't read the whole forum one so maybe they actually got it right later.

The 2nd link had many sample examples, I went through and just tried to see what was the most common thing about them. It seems (to me at least) that it's less about being engrossed in something and more of being a concept of "into" (either literally or figuratively).

In some cases you have to twist the logic a little bit in order for it to make some sense, but not sure there is a better explanation.

Edit: Basically what Tobberoth said

Tobberoth Wrote:申し込む - to be called in? to say in? Well, i'd say that 込む has the "into" meaning here, as in the third word, but more abstract.
買い込む - to be engrossed in buying
閉じ込む - to close in (to lock something up)

Obviously if you're going to be that literal it doesn't work. Languages don't transfer that way. But that in no way means these words are indecipherable without a dictionary. If you understand the general idea that -込む conveys, the compound verbs that use it are usually easy enough to figure out from context after seeing them once or twice.