Greek: anti, against; phone, voice: singing opposite, alternate chanting
1) A psalm or hymn sung in alternate chant by two choirs or by choir and congregation. A form of chant, introduced in the West about the 4th century gradually displaced the responsorial form.
2) A short verse or sentence sung before and after a psalm or canticle to determine its musical mode and to provide the key to its liturgical or mystical meaning. Antiphons are of three kinds: psalterial, from the psalm which follows; historical, from the mystery or festival; mixed, from the psalm and feast.
3) An anthem.
To double antiphon is to recite the entire antiphon both before and after the psalm.
To announce antiphon is to recite the antiphon before the psalm, only as far as the asterisk.