Source : Webster's Revised Unabridged Dictionary (1913)

Passacaglia \Pas`sa*ca*glia\, Passacaglio \Pas`sa*ca*glio\, n.
   [Sp. pasacalle a certain tune on the guitar, prop., a tune
   played in passing through the streets.] (Mus.)
   An old Italian or Spanish dance tune, in slow three-four
   measure, with divisions on a ground bass, resembling a
   chaconne.