Chant (4)
'chant' is the definition.
(synonyms)
This is all the clue.
(Other definitions for intone that I've seen before include "Recite as a chant" , "Recite without inflection" , "Speak in chanting voice" , "Recite in a chanting voice" , "Sing (prayer) on one note" .)
(Other definitions for incantation that I've seen before include "Charm" , "magic words" , "Formula" , "20 across" , "Magic spell" .)
'chant' is the definition.
(chant can mean to sing)
This is all the clue.
(Other definitions for sing that I've seen before include "Turn informer" , "Croon" , "Chorus" , "pipe" , "Confess" .)