CHIASMUS

Chiasmus is a poetic figure in which two words appear twice in the following order:

A B B A

For example, if you were to say

Whenever I stop to shop, I generally shop until I stop.

In this sentence, "stop" is your "A" term and "shop" is your "B" term. The words appear

Literary examples include the following from Hamlet:

King: Thanks, Rosencrantz and gentle Guildenstern.
Queen: Thanks, Guildenstern and gentle Rosencrantz.

[2.2.33-34]

Or consider the following lines from Milton's Paradise Lost:

Not that fair field
Of Enna, where Proserpin gathering flowers
Herself a fairer flower by gloomy Dis
Was gathered.

[4.268-271]