Full Idea
The four so-called 'causes' are the different types of item which figure in what Aristotle thinks are the four fundamental types of explanation of nature.
Gist of Idea
Aristotle's four 'causes' are four items which figure in basic explanations of nature
Source
report of Aristotle (Physics [c.337 BCE]) by Julia Annas - Ancient Philosophy: very short introduction Ch.5
Book Reference
Annas,Julia: 'Ancient Philosophy: a very short introduction' [OUP 2000], p.85
A Reaction
This interpretation now seems to be standard among modern scholars. The word 'aitia' translates as 'explanation', but it is important to remember that it also translates as 'cause'. Aristotelian explanations are essentially causal.