decani

Of the side of the chancel, apse, altar or choir on which the dean's stall is placed (the right hand side to a person facing the altar); decanal.

You want a few more daffs on the decani side […]

The higher of two choral voice parts sung when a part splits into two; traditionally sung by members of the choir on the decani side.

All the extant voices participate fully in the decani-cantoris split at that point, so one is tempted to assume that the tenors split into decani and cantoris parts as well.

That half of the choir singing decani parts, collectively.