ecphonesis

[ek-fuh-nee-sis] /ˌɛk fəˈni sɪs/
noun, Rhetoric
1.
the use of an exclamatory phrase, as in “O tempore! O mores!”.
Also called exclamation.
Origin
1580-90; < Greek ekphṓnēsis, equivalent to ekphonē-, variant stem of ekphōneîn to cry out (see ec-, -phone) + -sis -sis