poly - many
dáktulos - finger
Polydactyla: multiple finger (double notes) passages such as (possibly alternating) thirds, fourths, fifths, or sixths.
Pieces based on polydactyla: Chopin's Op. 25 Nr. 6, Liszt's Feux Follets, Schumann's Toccata.
In polydactyla passages such as thirds scales it is very helpful to practice (and play) the upper (leading) voice legato and the lower voice non legato.
See: 362 • Ill executed holding excises are futile fixations.
See: 285 • The pianist’s hand has six fingers
See: 252 • Chromatic scales fingerings