Theology is full of ologies. They’re often useful ways of quickly referring to whole subsections of theological thought, which is great for concision, but not so great for those who haven’t been inducted into the Mysteries of Jargon. Fortunately, the world of theology isn’t quite so bad as the Masons, so I shouldn't get into trouble for initiating you (phew).
Anyway, all ologies come from the Greek word logos (or λογος if you want to show off) which means ‘word’. So any ‘ology’ means ‘things we say about...’ whatever the ology-prefix is. Here, then, are some ologies for your delectation (the first of two posts - too many ologies all at once can be a bit much):
Aetiology: aitia means ‘cause, reason’ so aetiology is ‘things we say about causes and origins.’ Creation stories are all aetiological, insofar as they say things about the origin of the world. People often refer to creation stories as ‘aetiological myths’, which DOESN’T MEAN THEY’RE NOT TRUE, guys, so please don’t freak out on me.
Anthropology: anthropos means ‘human’ or ‘man’ (the OED seems unbothered by the sexistness of using ‘man’ to mean ‘mankind’ so it’s hard to tell just how gender-specific the word is), so anthropology is all about the study of humans and human nature. This looks quite different as a subset of theology than it does as a subject all on its own. A friend of mine did a degree in Anthropology, during which he spent several months living with monkeys. You don’t get to do that in theology.
Christology: G’won, see if you can work this one out for yourself. Well done! Have a sticker. Christology is all about Jesus, the God-Human, and what you get if you add the divine nature to the human nature and still end up with only one person. Was Jesus fully human? Was he fully divine? How did his humanness and divinity interact? It’s one big barrel o’ questions.
Epistemology: episteme means 'knowledge', so epistemology is the discussions and theories we have about what it means to know: what do we know, how much can we know, how sure can we be about what we know, whether there are different sorts of knowledge, and if so, which is better. Know what I mean?
Eschatology: eschatos means ‘last’, so eschatology is ‘things we say about the last things’. Eschatology is all about the End Times, or the weird stuff that happens in Revelation, or when Jesus will come back and what will happen (we’ll all look busy, right). It doesn’t have to be all Left Behindy, though: some people manage to write about eschatology without pooing all over biblical scholarship, good theology, and the English language (oooh, BURNED!).
Hamartiology: I once looked up hamartiology in the Oxford English Dictionary, and couldn’t find it. I was very excited to have discovered a word that the dictionary had missed, right up till the moment I realised I’d just been spelling it wrong. Boo. Anyway, hamartia means ‘sin’: so hamartiology is ‘things we say about sin’: is it all about pride, or missing the mark, or loving the wrong things, or the heart being turned in on itself; what is original sin and how does it affect us?
Missiology: The theory of mission, innit?