chiasmus
noun
chi·as·mus kī-ˈaz-məs 
kē-
: an inverted relationship between the syntactic elements of parallel phrases (as in Goldsmith's to stop too fearful, and too faint to go)
Example Sentences
Recent Examples on the Web Third, there are several instances of chiasmus, an A-B-B-A pattern. 
Sam Bray, Washington Post, 23 July 2017
Sam Bray, Washington Post, 23 July 2017 Word History
Etymology
New Latin, from Greek chiasmos, from chiazein to mark with a chi
First Known Use
1871, in the meaning defined above