Rhet.
[ad. Gr. {delta}{iota}{alpha}{sigma}{upsilon}{rho}{mu}{goacu}{fsigma}, Latinized diasyrmus, disparagement, ridicule, the rhetorical figure expressing this, f. {delta}{iota}{alpha}{sigma}{guacu}{rho}{epsilon}{iota}{nu} to disparage, ridicule, f. {delta}{iota}{gaacu} through, apart + {sigma}{guacu}{rho}{epsilon}{iota}{nu} to drag.]

A figure of rhetoric expressing disparagement or ridicule. -OED2

interesting, just today OED chaged the look of their online site. copying Greek terms now comes across as you see it, rather than being lost as before.

as to this word being rare, it isn't all that. OED2 has many words marked rare for which they have zero citations, or only a cite from a really old dictionary such as Jamieson or Bailey.