ephymnium

from The Century Dictionary.

• noun In ancient prosody, originally, a brief standing acclamation to a god following a number of lines or a metrical system in a hymn; the refrain at the end of a stanza in a hymn; in general, a short colon subjoined to a metrical system, strophe or antistrophe. See mesymnion, methymnion, proÿmnion.
• noun In the Greek and other Oriental churches:
• noun A line of separate construction at the end of a hymn or stanza of a hymn, often sung by other voices than those singing the remainder of the stanza or hymn.
• noun The repetition (of the antiphon).