I finally figured out the ending –지마: it means don’t [imperative]. It coalesced last night, as I was walking home, and I overheard two small boys playing, they were jumping off of a low wall along the footpath. One of them said to the other “하지마” (hajima – don’t do that). I have been familiar with this as a set phrase, but I had never successfully parsed it before into its component parts: ha [the verb to do] + ji [a verb-ending conveying conjecture or insistence] + ma [I think this is an informal intimate form of the verb 말다, meaning stop or cease]. So, at last I figured out that you can put –지마 (or the more formal –지마세요) onto any verb, in order to say don’t do X.
And the reason this finally clicked, for me, was because of another expression I’d learned yesterday from my students, and had been puzzling out: 얘들아 깝치지마 (yaedeura kkapchijima), which roughly means “you kids, stop being so obnoxious,” but the phrase is extremely informal, basically rude if not downright vulgar – so maybe a good idiomatic translation might be “y’all need to shut the hell up” (which is how an Army sergeant I once had used to introduce himself whenever he walked into a room, as a kind of signature phrase, and it was particularly humorous because he would say that, first thing, even when entering a room that was utterly silent).
Yesterday, I also found a great resource for learning abstruse tidbits of Korean language from a foreigner’s perspective: there’s a guy who’s been blogging (in English) his in-depth explorations of Korean for years now, at Korean Language Notes. He has a pretty academic orientation (which I find appealing given my own tendencies). I spent several hours surfing through old posts, though I’m at too elementary a level to understand all but some fragments of it.
I also successfully made use of naver.com’s Korean-Korean dictionary for the first time, which feels like a landmark of sorts – the ability to look up a word in Korean, and comprehend what it says about that word, in Korean. It’s a trivial step, but it felt like progress.